The hatching time of Moina irrasa sexual eggs at different temperatures is tested.According to the mathematical analysis of the relationship between incubating-out time (n) and temperature (t), the following conclusions are drawn. The function of n-t is;??? Function (1) represents the relationship of initial incubationg-out time and temperature.From this we calculate that the minimum threshold of development (T₁),thermal constant (Q), high sublethal temperature(t_s) and high lethal tempetature(t_D) are; T₁=l2.00℃ Q=441.61 C·h,t_s=35.16℃ andt_D=39.44℃.Function(2) represents the relationship between the incubating-out time of half amount of active eggs and temperature.Consequently the average of the above-mentioned ecological para-maters are obtained, i.e.:T=12.88℃, Q=557.10 C·h, t_s=35.50 0 and t_D=39.49℃ respectively. These ecological parameters can provide significant data for high and stable factory culturing of fresh water flea.