Abstract: Using extended FAST method, we quantitatively analyze the sensitivity of maximum tsunami wave heights to the seismic tsunami source parameters, on the assumption that an earthquake with magnitude M_W8.0 occurred at the northern fault segment along Manila Trench and triggered a tsunami in the South China Sea. The tsunami wave heights are computed based on the COMCOT model, and the investigated parameters are principally the earthquake’s magnitude, focal depth, epicentral location, strike angle, dip angle and rake angle. We also analyze the interaction effects of the above parameters on the maximum tsunami wave heights. The results of the sensitivity analysis indicate that the maximum tsunami wave heights of B₁(20.1°N, 119.4°E), B₂(18.4°N, 118.1°E), B₃(13.5°N, 117.6°E) are very sensitive to the earthquake magnitude, followed by the epicentral location, the strike angle and the dip angle. The interaction effects between the sensitive parameters are rather strong. But there exist differences in each parameter’s important measure order for different locations. Our result is significant to understanding the relationship between the tsunami wave heights and the seismic tsunami source parameters.