The normal working stability of 20-inch MCP-PMTs are studied by random triggering, in this paper. The variation of dark counting rate and gain in the long-term (∼400 days) aging process is mainly analyzed. It is found that the variation trend of the dark counting rate is consistent with the temperature, and the dark counting rate increases by about 15%/∘C at room temperature (20–28∘C). Moreover, the gain of PMTs began to decline after 5 months of continuous operation. After the gain is reduced by about 15%, the gain reaches a steady state.