With the exploitation of heavy oil reservoir，hydrogen sulfide released in the process of heavy oil thermal recovery continually increases. Especially in steam drive block，the discharge of hydrogen sulfide surges，detrimentally affecting the safety production of the heavy oil thermal recovery block. In order to further understand the mechanism of the generation of hydrogen sulfide in the process of heavy oil thermal recovery，factors such as the water content，the processing temperature and the processing time were tested. The results show that the transformation of different forms of sulfides to hydrogen sulfide can be maximized under the conditions of 20% of water content，260 ℃ of processing temperature and 48 h of processing time for the target heavy oil. In the process of heavy oil thermal recovery，mercaptan sulfur and thioether sulfur contribute to the generation of hydrogen sulfide，while thiophenic sulfur has no contribution. Analysis on contribution of different forms of sulfides to sulfide hydrogen produced in the thermal recovery of heavy oil can provide technical supports for the corresponding prevention measures in the exploitation of high sulfur block.