The solar gamma-ray are mainly produced by the hadronic interactions of cosmic rays with the solar atmosphere. Some theoretical works have been done to estimate the flux distribution of solar gamma-ray by Monte Carlo simulation based. In this work, we will estimate the solar gamma-ray emission based on Geant4 code. An approximate structure of the Sun and its atmosphere areconstructed in the code. The cosmic rays are generated at 600km above the solar surface. The gamma-ray are traced until they are absorbed or escape from the solar atmosphere. Finally, the flux and spectrum for observers on Earth are presented. Some comparison between our result and others are also discussed.