Type I/Type II angle-detuning tripling frequency scheme of KDP crystal was chose for triple harmonic conversion with large aperture and high power. Based on three-wave mixing nonlinear coupling equation, wrote a two. dimension program for numerical simulation triple harmonic conversion by introducing discrete Fourier transform and a fourth-order Runge-Kutta integrating method. With the code, conversion features and efficiencies of second and third harmonics were calculated with different thickness of crystal and different angle-detuning. The tripling frequency system is also optimized assuming the intensity distribution of 1ω is super Gaussian distribution with sixth-order. The results showed that the system has both broad dynamic range and more high conversion efficiency.