Abstract: The Muyudao 42 was a new early japonica variety with high yield in cold region bred by Mudanjiang Branch of Heilongjiang Academy of Agricultural Sciences, and it had the advantages of early maturity, high yield, good quality, disease resistance, lodging resistance and cold resistance.In this study, the parents of Muyudao 42 were traced back and the pedigree was constructed to analyze the main characteristics and nuclear genetic contribution rate of the parents, revealing the genetic evolution process, and providing reference for the selection and utilization of rice breeding parents.The results showed that the Muyudao 42 belonged to cytoplasmic family of Longjingchanglixiang, and the transmission route was as follows Longjingchanglixiang→Du 00-1066→Muyudao 42.The nuclear genetic material was provided by the ancestral parents Longjingchanglixiang, Fushiguang, Taizhong 27,Gaoxiong 53,Beihai 84,Sejiangke, Hexuan 58,Nonglin 11,Xiabei, Tijin, Aoyu 239,Quxi 17,Tengxi 117,Shishoubaimao and Xiayi in different proportions, and the nuclear genetic contribution rates were 25%,37.5%,0.585 937 5%,0.585 937 5%,0.585 937 5%,2.343 75%,4.687 5%,0.585 937 5%,2.343 75%,2.343 75%,respectively, 2.343 75%,4.687 5%,9.375%,1.171 875% and 5.859 375% respectively.The selection of parents should pay attention to the adaptability of the mother in the local area, while the father should have the genetic consanguinity of geographical or ecological distance.In conclusion, the narrow genetic base is the main limiting factor for new breakthroughs in rice breeding in cold region.