From Aug. 21 to Nov. 13 in 1999, the population density of Galerucella nipponensis was surveyed in the waterchestnut field at Guantian township, it found the highest population peak reached in the late August with 11.6 individuals per plant. The frequency of 8 eggs contained in a cluster was the highest, with 18%. There were two species of Tetrastichus parasitoid was found parasitized in the eggs, and average percentage of parasite was 57%. In test of the temperature effect on development of Galerucella nipponensis, it was showed that the eggs could not hatch at low temperature 10℃, the pupae could not complete development at 15℃, and the larvae could not finish development at 35℃. The higher the temperature was, the developmental duration was shorter under the optimal temperatures of 20℃ to 30℃.