We propose an improved design solution of large-aperture photon sieve. All the pinholes in one Fresnel ring are regarded as a whole, and the diffraction field formula is deduced after approximation and transformation based on the nonparaxial far-field pinhole diffraction model. The main work of this paper focuses on the internal condition of pinhole ring diffraction model. According to calculation, the diffraction field calculated by the pinhole ring model is basically consistent with that calculated by the traditional far-field pinhole model, the large photon sieve designed by the new method focuses well on the focal plane, and the computational efficiency is greatly improved. This method could benefit the flexibility of design and fabricating the larger aperture photon sieve.