The settling behaviors of rectangular particles with different initial orientation angles, aspect ratios and Reynolds numbers are simulated by using finite element arbitrary LagrangianEulerian domain method. The results show that the settling behaviors of the rectangular particle are affected significantly by the initial orientation angle under certain Reynolds number. With the increasing initial orientation angle, the fluctuation of the orientation angle, setting velocity，rotation velocity and lateral drifting velocity all increase. The impact of aspect ratio on the process of settlement has a strong relationship with the magnitudes of length and width. However, regardless of the magnitudes of length and width, when aspect ratio increased, final settling velocity decreases accordingly. Reynolds number of particle deposition process has a great impact on sedimentation process as well. If the Reynolds number is below a critical value, the particle eventually settles steadily. At larger Reynolds number，the oscillation of lateral motion and orientation angle become persistent. An inverted Tstructure forms due to the interaction between particles when many particles fall in the channel, and particles tend to horizontally positioned when the time span increases.