The light intensity distributions on pumped face and end surface in composite slab are simulated with the method of Non-Sequential Mode ray tracing using software Zemax.From the tracing results,we can find that when the pumping beam is on the pumped face,the light intensity distribution is homogeneous,but when it is on the end surface after transmitting through the undoped crystal the light intensity distribution is non-homogeneous.After investigation we find that the undoped crystal affects the pumping beam,that is to say,there is total internal reflection when the pumping beam is propagating in the undoped crystal,which induces the overlap of pumping beam in partial region of end surface,then induces the non-homogeneity of pumping beam distribution in the end surface.