Abstract: First,the condition under which the output signals of monopulse radar receiver with two Swerling 4 targets can be approximated to a Gaussian distribution has been studied and determined and it is little different from that in literature.Then the research on the approximate condition is extended to the case of multiple targets and the Maximum Likelihood(ML)+ Minimum Description Length(MDL) algorithm is adopted to estimate and detect them.The simulation results show that the performance of detection and estimation of multiple targets is acceptable under the approximate condition.