In 3D particle image velocimetry (PIV), when laser transports through dense trace particle field, scattering light intensity vary in different directions. In this article, we build 5 fields of different densities, and each field contains one vortex ring. The diameter of the vortex ring is 2mm, and the particles are dense in the ring and sparse outside the ring. Based on the Mie scattering theory and Monte Carlo method, we compute the laser intensity difference along the direction of incident light in each particle volume when the laser beam transports through it, and obtain the relationship of laser intensity, particle density and the distance of laser transportation. The variation of laser intensity could also be viewed from different directions. We also discussed the influence of light intensity variation on integrated imaging particle-imagevelocimetry (PIV) image’s quality in this paper. To deal with this variation, we propose a new light intensity equalized compensation method. By using this method, we can reduce the influence of attenuation when laser light transports through dense particle areas. During the simulation process, a camera array is set to detect the forward and back direction of the laser beam in the region, and the light intensity is recorded by different pixels. Light intensity attenuation of different positions is considered. All cameras are treated as pinhole models. The results show that front scattering and back scattering have great effects on integrated imaging PIV. The compensation method is used in experiment to preprocess particle images.