Abstract: A solar distiller based on nanofluid spectral splitting technique is proposed. The optical properties of modified disc-type distillers with different size are compared and analyzed by Monte Carlo method. The effects of solar altitude angle and azimuth angle,geometric parameters of distiller and inclination angle of glass cover on the optical efficiency and spot uniformity of distiller are studied.The results indicated that the optical efficiency and spot uniformity are approximately symmetrical in the morning and afternoon. The optical efficiency and spot uniformity of the distiller are the greatest at noon. The intensive irradiation on the bottom surface of the distiller is produced by the direct incident light. Increasing the length of distiller and decreasing the height of distiller are both effective ways to improve the optical efficiency and the uniformity of light spot. With the increase of the inclination angle of the glass cover,more incident light will be reflected to the outside of the distiller due to the increase of the back plate,thus reducing the optical efficiency.