We evaluated the relationship between sinking depth and a number of factors using multiple regression to determine the external patterns of sinking a purse seine. We collected data on sinking depth, gear operation, and shooting duration(), current direction() length from tuna purse seiners owned by Shanghai Fisheries General Corp. between September and December in 2011. Current direction and shooting velocity had no effect on sinking depth (). Conversely, the shooting duration, current speed, and length of the purse line had a significant effect on sinking depth (158. Principal component analysis suggested that the majority of factors associated with gear operation have little effect on the sinking depth. Under normal operating conditions (shooting duration: 550 s ,purse line length: 2 000 m), the model predicts that the average sinking depth is 236.78 m with a95% confidence interval ranging from of wind and currents. Similarly, the % confidence interval: 60.56 to 123.97 m)