To improve the thermal environment comfort of the manned submersible chamber, the thermal environment characteristics of cabin thermal environment were analyzed by the thermal comfort model of predicted mean vote-predicted percentage of dissatisfied(PMV-PPD). Based on the cabin environment data of 7000-meter task, the dynamic environment characteristics of the typical task stage were analyzed, and the key data about human and environment were obtained. By calculation of PMV-PPD by Matlab and further comparison of the index, the thermal comfort dynamic characteristics and distribution characteristics were investigated. In addition, optimization analysis of cabin thermal comfort was carried out regarding two controllable factors, wind speed and clothing thermal resistance. Results show that the PMV value was constantly changing between [-2, +2], and the thermal comfort of the pre-mission was characterized by the heat. Among them, 84% of the mission stage cabin thermal comfort was poor, of which 79.69% was cold and 16% was hot. Wind speed v and clothing thermal resistance Icl were important influencing factors for the regulation of thermal comfort in airtight cabin. For the manned submersible system lack of air conditioning, when the wind speed maintained 0.5 m/s in the control thermal environment stage and clothing thermal resistance increased by 0.93~1.48 at the cooling environment stage, clothing thermal resistance could effectively improve cabin thermal comfort.