【Abstract】 Objective To observe the change of protein in the hemlymph and DNA and RNA in the tissue from the 3rd stage larva of Musca domestica  before and after diapause. To explore the biochemistry mechanism of M.domestica larvae diapause. Methods The diapause of  the 3rd stage larva of M.domestica  was inducted by low temperature.（1）The change of hemlymph protein in the diapause and the nondiapause groups were observed by polyacrylamide gel electrophoresis?SDS. （2） The RNA and DNA in the tissue of the diapause and the nondiapause groups were extracted and the contents were determined by ultraviolet spectrophotometer. Results （1） The numbers of protein straps in the diapause groups  were similar to that in nondiapause group.But the content of the protein in the groups after diapause for 20 d was obviously higher than that in the  nondiapause group. The optical density value was 203 475.69 at 85 kd.（2）The DNA content in all diapause groups was much lower than that of nondiapause group. The RNA content obviously decreased after diapause for 10 d and 15 d, but it obviously increased after diapause for 20 d. The contents of RNA and DNA after diapause for 10 d and 15 d decreased to 0.598, 0.546 μg/mg, but they increased to 1.337 μg/mg  after  diapause for 20 d.   Conclusion Perhaps  there  was no diapause associated protein in diapause M.domestica larva. The decrease and increase of the proportion of RNA to DNA could be as the signal of beginning and ending of M.domestica larva diapause.