In order to study the influence of oxide aperture diameter on the characteristics of 940 nm vertical cavity surface emitting laser (VCSEL), 940 nm VCSELs with varied oxide apertures were fabricated, and then tested for analyzing. The gain of the quantum wells with different candidate barrier materials was simulated by PICS3D software, and InGaAs/AlGaAs was selected because of the higher gain. Moreover, the gain-cavity mode detuning was introduced in the design. On the basis of optimization, 940 nm VCSELs with six oxide apertures were fabricated and their photoelectric output characteristics were tested. The results show that the VCSEL with 4 μm oxide aperture achieves a slope efficiency of 0.93 W/A at room temperature and a maximum power conversion efficiency of 40.1%. For VCSEL with 7 μm oxide aperture, the maximum output power reaches 12.24 mW at room temperature. The VCSEL with 2 μm oxide aperture can operate on the fundamental transverse mode condition with maximum output power of 2.67 mW at room temperature, and maintain the fundamental transverse mode with a side-mode suppression ratio greater than 45 dB at 2 mA continuous injection current, on the working temperature from 10 ℃ to 80 ℃.