Pacific cod (Gadus macrocephalus) belong to a large group of fishes in the family Gadidae and order Gadiformes. The Pacific cod is an important commercial food species. The Pacific cods are found from the northern Yellow sea in China through the Bering Sea as far as the Chukchi Sea, and south along the Gulf of Alaska and the coast of North America to Monica Bay California. Pacific cod is one of the most important commercial fish after the Atlantic cod. Yet very little is known about population subdivision within and between management areas. In the Present, there is no comprehensive understanding of the numbers and distributions of Pacific cod stocks, although numerous stocks have tentatively been identified. Pacific cod have been placed in as few as two stocks across the species range or as many as ten in Asia alone. The detection of stable genetic differentiation indicating restricted gene flow provides the most stringent means to identify largely self-recruiting stocks. Surprisingly, few genetic studies of Pacific cod have been conducted compared to the congeneric Atlantic cod. In this study we have studied the Morphological and genetic study of Gadus Macrocephalus of the Bohai Sea, Yellow sea and the Sea of Japan. 　　In the first part we did the Morphometirc study for the morphological understanding of the Pacific cod. We studied the amount of morphological variation among three Pacific cod populations (100 individuals) was examined by the multivariate analysis of eleven meristic traits and twenty four morphological variables. From three geographically distinct areas the specimens were collected. The several statistical analyses were performed like principal component analysis (PCA), cluster analysis, one-way ANOVA and discriminate analysis. The discrimination accuracy was 79.2％-100%among three populations in which Qingdao population showed the 100% accuracy. The average discriminate accuracy was 88%. The value of theparameters and the cumulative contribution rate of the eight principal components was 81.72%. Scatter plots of scores on the first and second morphological parameters showed that there was scares overlap in three populations. Whereas One-way ANOVA showed the significant differences (P=0.05) among three populations based on some variables and coefficients of difference. According to the Mayr’s 75%rule, the results indicated that the difference between two groups (Lidao, Dalian) and other group (Qingdao) was a slight difference. It indicates that Lidao and Dalian populations are more closely related to each other than the Qingdao population. 　　The second part we had studied the molecular part for the better understanding of the fish populations among the Chinese and Japanese waters. In this study the genetic diversity of the Gadus macrocephalus from four populations indicated that the samples are divided in to two groups:Qingdao, Lidao and Dalian from Chinese water and the Sea of Japan. The mismatch distribution between haplotypes showed that the observation frequency is well fitted to the model frequency, which is a good verification to demographic hypothesis. In the Haplotype network for Gadus macrocephalus haplotype H1 represent the ancestral haplotypes that survived a population bottleneck or an episode of selection. PairwiseΦst and associated P values indicated that Sea of Japan population could be separated from other populations at genetic level. Within the populations represents the molecular variation among populations, the larger the value is, the more variance among populations. Among groups evaluates the molecular variation among groups that we have defined. Like the within the populations, the larger, the more variation exists between groups. What is also very important is the P value, which indicates how we can tell the value is large enough to be significant. So we tend to believe that within populations’ variance is the dominant reason for molecular variation, and no obvious population structure is detected from the four populations.