As an active detection method, the positioning performance and vertical accuracy of spaceborne laser radar are superior to inactive method. On account of the energy constrain on space, the laser radar operation mode need to be researched for imaging in high probability. In this paper, the influence of system detection probability resulted from the multi-pulse emission mode under the same total power is studied, and provided the detection probability equation in both cases as noise signal and no-noise signal. With the principle of mean squared error, this paper researched the multi-pulse detection error. Finally, above conclusions are simulated in numerical method. The results indicate that the detection advantage in multi-pulse mode become more remarkable with the increasing noise signal.