This paper explores displacement mechanisms of the residual oil film in microchannels by analyzing the following items after wetting hysteresis occurs: resistance on the residual oil film by the rock wall, the interfacial tension between displacement fluid and residual oil film, and horizontal stress acting on residual oil film by displacement fluids. Based on the continuity equations, motion equations, and constitutive equations of viscoelastic fluid, the numerical simulation is used to calculate the distribution of horizontal stress acting on the residual oil film by displacement fluids with different rheological properties. The results of the study show that increasing the horizontal stress on the oil film fundamentally mobilized the oil film and made it movable. Under the condition that the flow rate of the displacement fluid was constant, the value and direction of the horizontal stress acting on the oil film by the viscoelastic fluid changed. The elasticity changed the law of stress on the residual oil film, which is more conducive to mobilizing the oil film.