In order to explore the optimal heating temperature of the InGaAs photocathode, the high-temperature cleaning experiments were carried out at different temperatures by using the ultra-high vacuum interconnection setup for photocathode preparation and characterization, and Cs/O activation experiments were followed. By scanning focused X-ray photoelectron spectroscopy, in-situ analysis of InGaAs samples after chemical cleaning, heat cleaning, and surface activation was performed, to detect the desorption of surface impurities and the change of chemical element composition at different temperatures. The results show that the carbon contaminants and oxides are completely removed at 625 ℃, resulting in an atomically clean surface. However, the In element is volatilized at this time, which leads to the decrease of In composition and makes the infrared response of InGaAs material unobvious. Therefore, 600 ℃ is treated as the optimal heating temperature. Combined with in-situ ultraviolet photoelectron spectroscopy, it is found that the secondary electron cut-off edge continuously shifts towards higher binding energy as the temperature rises, indicating that high temperature cleaning can effectively reduce the work function. After Cs/O activation, the work function value is further reduced, and the negative electron affinity state is achieved, which improves the near infrared photoemission performance of the InGaAs photocathode.