Uniform steam chamber expansion over the whole well length significantly affects the development of steam-assisted gravity drainage (SAGD) in oil reservoirs. Currently, most research is focused on optimizing the steam suction profile through the production wells. While uniform steam injection (USI) along horizontal wells is often neglected and studied in only a few reports, it is a critical technique to enhance oil recovery. Herein, a novel type of USI-SAGD process using an injector tube with variable density perforation was developed. The performance of USI-SAGD was evaluated based on a custom-built physical experimental setup and numerical simulation. The experimental findings demonstrate that the USI-SAGD method exhibits a more homogeneous steam injection profile by mitigating the accumulation of wellbore fluids and, thereby, making the steam injection profile more uniform. This resulted in a notable increase of 22.6% in the uniformity of steam chamber development and an 8.02% increase in oil recovery compared with the single-point SAGD method under identical experimental conditions. Numerical simulations indicate that USI-SAGD effectively regulates the outflow profile and mitigates the decrease in steam quality caused by steam overlay along the injector. As a result, the method achieves an even distribution of the pressure and steam quality, which corresponds to an improvement in steam injection uniformity. The perforating point number and distribution were optimized, which indicated an optimal critical value of 30 perforating points per 1000 m wellbore and a 4:6 distribution ratio for improving the uniformity of the steam chamber and enhancing the production performance in the horizontal well. This work proves that USI-SAGD is efficient in improving heavy oil production and has great potential for use in field applications.