This paper presents the menstrual disorders produced by implantation of Norplantin women during a course of five-year usage. Total 1000 women were recruited. Themain side thects consisted of changes in bleeding patterns, including: menostaxis, hxpomenorrhoea, spotting,frequent menstruation, lnfrequent menstruation, amenorrhoeaand menorrhagia. Authors of this paper suggested that all the above-mentioned men-strual disorders could be explained by mathematical methods. Except for the incidenceof menorrhagia which revealed a negative linear correlation with the implantation timeinterval (correiation coefficient is - 0. 98), all the other six patterns of the abnormalbleeding changes could be fitted by the hyperbola model, because their incidencesreached a very high value in 3~ 6 months after implantation, then sharply dropped toa lower value at the end of one year, whence in turn were reduced slowly but progres-sively to the the end of the 5 th year. The results of all F tests were statistically signWicant (P< 0.01). The advantages of this curve fitting method are: 1, to show the re-lationships between the mismenstruational rates and time afer implantation of Norplant at a theoretical level; 2, to make a direct image; 3, tosmooth the values of the ob-servation and decrease the sampling variation; 4, to estimate the incidences of mismen-struation at a given time; 5, to tell women the changing rule of mismenstruations anddeveloping prospect before and after the implantation in order to increase their confi-dence and meanwhile to increase the conlinuous using rate. This paper presents the menstrual disorders produced by implantation of Norplantin women during a course of five-year usage. Total 1000 women were recruited. Themain side thects consisted of changes in bleeding patterns, including: menostaxis, hxpomenorrhoea, spotting, frequent menstruation, lnfrequent menstruation Authors of this paper suggested that all the above-mentioned men-strual disorders could be explained by mathematical methods. Except for the incidence of menorrhagia which revealed a negative linear correlation with the implantation time interval (Correction coefficient is - 0.98) , all the other six patterns of the abnormalbleeding changes could be fitted by the hyperbola model, because their incidencesreached a very high value in 3 ~ 6 months after implantation, then sharply dropped to a lower value at the end of one year, whence in turn were reduced slowly but progres-sively to the the end of the 5 th year. The results of all F tests were statisti The advantages of this curve fitting method are: 1, to show the re-lationships between the mismenstructive rates and time afer implantation of Norplant at a theoretical level; 2, to make a direct image; 3, tosmooth the values ​​of the ob-servation and decrease the sampling variation; 4, to to estimate the incidences of mismen-struation at a given time; 5, to tell women the changing rule of mismenstruations and development prospects prospect and after the implantation in order to increase their confi-dence and meanwhile to increase the conlinuous using rate