The paper reports the identification of the causal organism of root rot of muskmelon (Cucumis melo) in Beijing and its biological characteristics.The results showed that the causal organism was [Fusarium solani (Mart.) Sacc.] ; the range of temperature for its mycelial growth was 5-40℃,the optimum at 30℃; it could grow at the range of pH4-12,pH7 was the optimum ; the pathogen could utilize many kinds of carbon resoiurce very well,and NaNO3 and Ca(NO3)2 were its best nitrogen nutrition; the hypha lethal temperature was 60℃,10min; the conidia germination rate was the highest in the water drop and conidia could not germinate if the relative humidity was lower than 90%; the conidium lethal temperature was 57 ℃,10 minutes lasted.