In this paper, the flat type of CFEL partialy loading dielectric with wiggler is studied using two dimensional kinetic coupling mode theory of three waves. It is shown that the system for arbitary thickness of dielectric can generate short wavelength coherent radiation by using low energy electron beam. Suitably choosing the system parameters, the growth rate of the kind of CFEL may be much higher than general FEL and CFEL. It is also shown that the main mode of super radiation in the system is LSE mode.