Abstract: 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. Tripling frequency system assuming that the intensity distribution of 1ω is super Gaussian distribution with sixthorder is optimized. The results showed that the system has both broad dynamic range and more high conversion efficiency.