According to the measurement equation of interferometric particle imaging(IPI), the influence factors including the maximum and the smallest measurable particle diameters and its measuring accuracy of particle diameter, are analyzed in IPI optical system. For the given CCD, imaging lens, wavelength of illumination light and the thickness of the laser width, the influence of the object distance and defocusing distance on the size of the interference pattern of a particle is thoroughly analyzed, the measuring accuracy and the measurable range of particle size are then investigated. The result is that the relatively larger collection angle should be used as much as possible on the condition that the requirements of the measurable size range are satisfied. The larger the size of the interference pattern, the smaller the measuremental error of particle size with the finger overlap considered, and the sub-pixel accuracy of the number of fringes/finger spacing is acquired by interpolation. The optical system design example and its test results of the standard particle are given.