The design of the microstructure distribution on the bottom surface of the partial integrated light guide plate (PILGP) is one of the key factors to improve the luminance uniformity of the partial integrated backlight module (BLM). In this paper, the two-dimensional micro-prism expressions on the bottom surface of the small-sized PILGP are presented. The two-dimensional micro-prism expressions make the micro-prisms spread out on a two-dimensional scale of the bottom surface of the PILGP. By fitting and analyzing a large number of simulation data, the relationship expressions between the coefficients of the two-dimensional micro-prism expressions and the structural parameters of the PILGP are established. The above expressions are directly applied to the two-dimensional distribution design of micro-prism on the bottom surface of small-sized PILGPs with different structural parameters. Without the help of the designers’ experience and the multiple simulations of the software, the average value of luminance uniformity in the partial integrated BLMs is obtained to be 84.94%. The simulation results show that the two-dimensional micro-prism expressions and coefficient relation-expressions presented in this paper have important application value. Take the 5-inch partial integrated BLM for example. The two-dimensional distribution of the micro-prism on the bottom surface of the PILGP with high luminance uniformity can be obtained directly by using the above expressions. By fine-tuning the coefficients of two-dimensional micro-prism expressions, calculated by the coefficient relation-expressions, the utilization of light energy, illuminance uniformity and luminance uniformity of the partial integrated BLM respectively reach 90.69%, 88.02% and 92.17%, which meet the practical requirements. The optimization and design time of the partial integrated BLM are both greatly saved. Further, the two-dimensional micro-prism expressions on the bottom surface of the PILGP are analyzed and the physical mechanism is explained reasonably. This work is of significance for the distribution design of the microstructures on the surface of the LGP.