A LED flat panel light without light guide plate was designed to solve the disadvantages of low luminous efficiency and the high cost of Light Guide Plate(LGP) in edge-lighting LED flat panel light. The beam launched from the LED arrays was converged by the compound parabolic reflective cup(CPC) and was gazed on light emitting panel. In this way, the uniform luminous can be obtained on light emitting panel. Then, Taguchi method was used to design the experiment and analyzed the factors that affected maximum and uniformity of illumination by the software of Tracepro simultaneously. Furthermore, the influence of quality was studied by the theory of ANOVA to optimize structural parameters. Finally, the LED flat panel light without light guide plate after optimizing was designed with the illumination uniformity of 95.87% and the maximum illumination of 39 870 lx. These results show that the flat panel light that designed has achieved the general or even better effects of LED flat lights. It can also largely reduce the production cost of LED flat panel lights owing to the design of removing LGP. Besides, the applying of Taguchi method greatly simplified the design processes.