Achieving high efficiency and power output for 1 550 nm Vertical Cavity Surface Emitting Lasers (VCSEL) remains a challenging issue. In the content of VCSEL, optimizing the oxide aperture size has been shown to enhance output power and slope efficiency. Additionally, multi-junction has emerged as a promising approach to boost the VCSEL chip power. The integration of these two techniques for 1 550 nm VCSEL has the potential to optimize their output characteristics. This study builds upon previous researches on 1 550 nm multi-junction VCSEL and investigates their combination with oxide aperture structures. The primary focus is on output power, slope efficiency, and photoelectric conversion efficiency. Different structures with varying oxide aperture sizes are simulated and analyzed detailedly to achieve high-power VCSEL with improved performance. The differences in output characteristics between single-junction VCSEL with and without an oxide aperture layer between the active region and N-type Distributed Bragg Reflector (DBR) were investigated before. The main comparison parameters are output power and slope efficiency. Two different oxide aperture structures are simulated and compared, the results show that VCSEL chips without an oxide aperture layer between the active region and N-DBR exhibit higher output power and slope efficiency. At an oxide aperture size of 11 μm, a single-junction 30 μm VCSEL demonstrates a threshold current of approximately 1 mA and an output power of about 57.2 mW. Furthermore, during the investigation, the simulation results can be indicated that as the oxide aperture size increases, the chip's lasing wavelength experiences a red-shift phenomenon, with a maximum red-shift of up to 6.5 nm. However, beyond an aperture size of 14 μm, the lasing wavelength hardly red-shifts. To address this shift issue, the thickness of the spatial aperture layer is adjusted to tune the chip's lasing wavelength to around 1 550 nm. Based on these findings, the paper delves into the exploration of multi-junction VCSEL. Due to the unique structure of the active region in multi-junction VCSEL, the paper considers the feasibility to add an oxide aperture layer within the active region during chip design. The oxide aperture size is adjusted and simulations are conducted to compare the output power, slope efficiency, and photoelectric conversion efficiency between the two structures. The results show that both structures achieve higher output power at an aperture size of 9 μm. For the single-layer structure, the output power reaches approximately 177.55 mW at 100 mA, with a slope efficiency of 1.79 W/A, and the maximum power conversion efficiency of 37.7% is achieved at a 10 μm aperture size. The multi-layer structure exhibits even higher slope efficiency, reaching 2.36 W/A. The comparison of simulation results shows that although the proposed multi oxide layer structure can achieve the goal of improving power, the conversion efficiency is not higher as well, which is also related to the high applied voltage. The research in this paper demonstrates the potential of oxide aperture structures in further improving parameters such as power and efficiency for multi-junction VCSEL. The combination of oxide aperture integration and multi-junction structures can provide a reference for optimizing the output characteristics of high-power 1 550 nm VCSEL, making them highly desirable for various applications in the fields of communications, sensing, and optical interconnects.