Cao proposed that recurrent light scattering(multiple scattering forming close loop)results in the random laser with coherent feedback. She hasn't indicated the lasing relative probability of the close loops which are formed by different numbers scattering particles. For simplicity a model is proposed,in which ZnO scattering particle is cube and the only one of six surfaces is mirror. For the random laser with coherent feedback arising in laser dye solution containing ZnO nanoparticles or arising in ZnO powder film,according to the analysis and calculation,it is showed that the lasing is much easier to arise in the two-particle closed loop path than in the three-particle closed loop path,and the lasing is more difficult to arise in the closed loop path which contains more particles. The result is agreement with the experiments.