Blue-green laser has broad application prospects in non-acoustic detection of underwater targets. However, the existing detection models have not considered the problem of matching the detection probability with the self-guided system. A target detection model of underwater laser scanning detecting system was established based on undershoot distance to match the guiding precision. The simulation results shows that an increasing undershoot distance needs an increasing emit angle to get high detection probability at a certain emit frequency, which however leads to a decreasing acting time for the following system. In addition, an increasing undershoot distance needs an increasing emit frequency and a decreasing step angle to avoid missing the target. Finally, the simulation provides an optimal range for undershoot distance and system parameter. The model and the simulation results provide theoretic basis for the matching up design of guiding system and detecting system.