Abstract: To investigate the optimal conditions for the tetraploid induction of the Pacific oyster Crassostrea gigas “Haida No. 3” by cytochalasin B (CB) and low salinity, the effects of CB concentration (0.2, 0.4, 0.6 and 0.8 mg/L), low salinity (6, 8, 10 and 12) and induction duration (10min, 15min, 20min and 25min) on the cleavage rate, hatching rate, tetraploid rate and the efficiency of tetraploid induction were estimated by inhibiting the first polar body of fertilized eggs. At the same time, the growth and survival of the larvae were analyzed. The results showed that the maximum point of tetraploid rate (65.69±2.47)% and the efficiency of tetraploid induction was found at CB concentration of 0.6 mg/L and induction duration of 15min. In low salinity group, the maximum point of tetraploid rate (38.77±2.69)% and the efficiency of tetraploid induction was found at salinity of 8 and induction duration of 15min. The shell height of CB and low salinity groups were larger at the early stage and smaller at the later stage compared with the control group. The shell height of the CB treatment group was significantly greater than the low salinity group (P<0.05), and the mean daily growth of larvae in the CB and the low salinity groups was (14.2±1.08) μm/d and (10.49±0.60) μm/d, respectively, which were smaller than the control group (15.43±1.08) μm/d. The survival rate of the two induction treatment groups was consistently lower than the control group, and the survival rate of the low salinity group was higher at the early stage and lower at the late stage compared with the CB treatment group. In general, the CB induction method showed better results in terms of tetraploid rate, the efficiency of tetraploid induction, 12-day survival rate and growth rate, and has better applicability for the tetraploid induction of the Pacific oyster “Haida No.3”.