Abstract: This paper deal with the difference of chemical compoition in different host tree under different kind strain,age and whether the lac insect take in nutrition from bark of host tree and the influence on chemical composition of branchs suitable for growing lac insect under a great number of blossom and bearing fruit.The result shows that there are tannin and phenol in many species of host plant.Contrast branchs in which lac insect are parasitized with branchs in which lac insect are parasitized have ceported that contents of tannin in branchs with lac insect is 5.36%.It is more than the contents (4.06%) of branchs in which lac insects are parasitized.But contents of sugar are contrary. A great number of blossom and bearing fruit of host plant can reduce the content of inorganic element in branchs.It can also affect synthesis and transport of carbohydrate,amino acid etc in nutritive organ of plant. This will affect growth and secreting lac of lac insect.Treat with wiping out flower buds can enhance the contents of organic substances in branchs suitable for growing lac insect.Thus it can promote quality and output of seed lac in winter generation.