Abstract: In order to obtain suitable conditions for tetraploid induction of Crassostrea gigas “Haida No. 2”, the effects of cytochalasin B (CB) concentration, initial induction time and induction duration on tetraploid rate and D larvae rate were estimated. The ploidy of induced spat was tested to verify the effectiveness of the induction method. The result showed that the linear effects of CB concentration and initial induction time on tetraploid rate were significantly (P<0.05), but induction duration had no significant effect on tetraploid rate (P>0.05). The interactive effect of CB concentration, initial induction time and induction duration influenced tetraploid rate significantly (P<0.05). The linear effects of CB concentration, initial induction time and induction duration on D larvae rate were significant (P<0.05), but the interactive effect of CB concentration, initial induction time and induction duration had no significant effect on D larvae rate (P>0.05). The maximum point of tetraploid rate was found at CB concentration of 0.5 mg/L, initial induction time of 15min and induction duration of 20min. Under these conditions, the tetraploid rate reached to (37.82±4.75)%. On day 180, tetraploid spat of C. gigas “Haida No. 2” existed in two of the treatment groups, and the tetraploid rates were 2.22% and 3.03%, respectively.