To solve the high temperature problem of new ratchet ultra-compact combustor, a full-coverage film cooling method was adopted. Based on the experiment and simulation of KJ-66 micro gas turbine, the original combustor was replaced with a ratchet ultra-compact combustor after scaling optimization. Then, according to the high temperature wall of the slope of the sudden expansion section and the inner ring in the secondary combustion zone, the influences of different arrangement modes, hole inclination angles and expansion film holes on the film cooling effect under actual combustion conditions were compared. The results showed that the film coverage of the cylindrical film holes on the slope of the sudden expansion section was not ideal, the comprehensive film cooling effect was not good, and different arrangements and hole inclination angles had little influence on the film cooling effect. The air film adhesion and cooling effects of the slope were greatly improved by expansion film holes. In the expansion film holes with 45° hole inclination angle and 0.6 mm outlet diameter, the comprehensive cooling effect produced by blowing off the high temperature flame surface and overlaying the air film was the best. Under the influence of the mainstream high centrifugal force field, the downstream of the secondary combustion zone could also obtain better adhesion effects of film when the blowing ratio was larger. The influence of the arrangements on the film cooling effects in the secondary combustion zone was more obvious than that of the hole inclination angles. On the whole, the full-coverage film cooling has good cooling effects on the wall of the ratchet ultra-compact combustor under actual combustion conditions. Expansion film holes can effectively improve the film cooling effects.