For purpose of revealing the negative impacts of multiple primary aberrations in high numerical aperture optical system, the combined influence of the primary aberrations, especially coma, astigmatism and spherical aberration, on focusing Gaussian beam in high numerical aperture system was carried out based on diffraction theory. The intensity distribution of the Gaussian beam focal spot suffering multiple influence of coma, astigmatism and spherical aberration were acquired by numerical simulation. The results show that the impact of multiple abrration was not only superimposed of single aberration. In addition, a high consistency was found between the simulation results and the laser spots captured on the focal plane of a self-made high numerical aperture system, which indicated the reliability and reasonableness of the numerical simulation. The results present the optical distribution properties of Gaussian beam receiving multiple primary aberration effects, which will be helpful for evaluating and analyzing the practical optical focusing system.