Abstract: To observe the light spectrum of the gas puff imaging (GPI) on experimental advanced superconducting tokamak (EAST), a GPI diagnostic optical window was designed. Based on the initial structure of the Petzwal lens,the optimization of the system was conducted. The aberration of the designed system was controlled within 1/4 ,and the modulation transfer function (MTF) was 0.76 at 16 lp/mm with the wavelength of 656.2/587.6nm. Then the multiconfiguration at the temperature of 20~250 was analyzed，the lens material which had the similar coefficient of thermal expansion was selected, and the MTF at 16 lp/mm was almost invariable in T direction, but it was changed from 0.82 to 0.69 in S direction, which was still in the design range. In addition, according to the physical environment of the optical window, the statics and the thermodynamic simulation was done to the window, the deformation of the window was 1/5 , the tolerance analysis based on the value of the deformation showed that the optical systems MTF was still bigger than 0.5. Finally, the spectral images captured by rapid camera showed that the distribution and the change of the intensity could be clearly observed by the optical system.