Abstract: Particle size distribution (PSD) represents the variation of the particle number with the particle size. PSD information is important in explaining the marine carbon cycle and quantifying ecosystem structure and function. In this paper, based on the two cruises in the coastal waters of Qinhuangdao during the summer and autumn of 2017, the effect of reference diameters on PSD was studied, and the characteristics of PSD in different seasons were discussed. It was found that the power-law model was suitable for describing PSD at most monitoring stations, and different reference diameters significantly influenced the simulation accuracy and PSD slope. The reference diameters should be larger than 26.7 μm in summer and 61.2 μm in autumn, the Mean Absolute Percentage Error (MAPE) for these range were the smaller, respectively. At the same time, combining the results of PSD slope, the optimum reference diameters in summer and autumn were 43.9 μm and 85.2 μm, respectively. On this basis, the PSD slopes of the sea surface over the coastal waters in summer and autumn were at the range of 2.44～4.62 and 2.30～3.76. The average particle size in autumn was higher than that in summer. In addition, we studied the relationship between PSD slope and the spectral slope of particulate beam attenuation. It showed a good linear relationship, with correlation coefficients R² of 0.63 and 0.68 in summer and autumn, respectively. The conclusion of this paper provides a good theoretical basis and technical support for PSD inversion using remote sensing.