Taking the roughness into consideration, this chapter mainly studies the isothermal elastohydrodynamic lubrication between the slider and the balls in the new three-pronged universal joint and gives the relevant equations under isothermal conditions. The Reynolds equation is the primary tool for iteration, and Matlab is used for programming and plotting. In the simulation experiment, the roughness is given as 0. Then the amplitude and frequency of the roughness are varied to observe the oil film thickness and pressure respectively. With the increase of surface fluctuation, the film thickness in the center of the contact range becomes thicker, the pressure changes more and more sharply, and the peak value of secondary pressure is basically unchanged. As the frequency of the sinusoidal roughness increases, the film thickness in the center of the contact area becomes thinner as the frequency of roughness enhances, the fluctuations become more and more frequent, the pressure fluctuates around the original curve more and more often, and the amplitude becomes larger and larger.