Flexible III-V thin-film solar cells are usually used as space power supply in spacecrafts. In practical applications, suitable encapsulated materials can protect the cells from being affected by environmental factors such as moisture, oxidation and pollutants. Therefore, it is critical to explore suitable flexible encapsulation schemes and long-term stability of solar cell performance. In this paper, the prepared flexible GaInP/GaAs solar cells are welded by resistance welding, and then laminated with polymer encapsulation thin films and hot melt adhesives with high light transmission. After being encapsulated, the flexible two-junction solar cell achieves good electrical performance (J_sc = 13.105 mA·cm^–2, V_oc = 2.360 V), the photoelectric conversion efficiency can reach 24.81%, and the weight density is about 405 g/m². The performance stability and environmental tolerance of the encapsulated flexible GaInP/GaAs solar cells under complex storage conditions are investigated. The results show that the encapsulated flexible solar cells still maintain good stability after 85 ℃/85% RH damp heat has been tested for more than 1000 h and 108 cycles of thermal cycling test between –60 ℃ and 75 ℃, respectively. It also proves that the encapsulated technology adopted in this experiment is feasible and has an excellent protective effect on the double-junction solar cells. However, there is a slight decrease in the open-circuit voltage in the long-term damp heat test (ΔV_oc ≈ 0.023 V), which may reflect the change of the solar cell itself. By further extracting the changes of the ideal factors n₁ and n₂ representing the recombination mechanism and diffusion mechanism respectively from the dark I-V curves (Δn₁ = 1.295, Δn₂ = 0.087), it can be found that the slight drop of open-circuit voltage is closely related to the recombination enhancement (Δn₁\gg Δn₂). In the long-term high temperature and humidity environment, it is easy to introduce defects in the material of the solar cells, serving as the carrier recombination centers, thus accelerating the carrier recombination, reducing the parallel resistance, shortening the minority carrier lifetime, and increasing the reverse saturation current resulting in a slight drop in the open-circuit voltage. In addition, the electrical simulation results based on the diode-model indicate that the change in the performance of the solar cells after flexible encapsulation is due to the enhanced carrier recombination under damp heat test, which reduces the open-circuit voltage.