A brief introduction to cosmic muon physics is presented. We focus on the basic principle of coincident counting of cosmic muons in the physics laboratory. We introduce the method of Monte - Carlo ( MC) simulation in particle physic，including selection of physics lists，optimization of detector materials and geometries，inputs and outputs of the simulated data. We also discuss the preliminary results muon decay spectra where the fitted muon life-time matches the theoretical prediction. The established MC simulation tool is of pedagogic significance for it helps better students’insight into the cosmic muon physics.