Novel coronavirus pneumonia in 17 city (Hubei) provinces was analyzed by using the principle of thermodynamics. A thermodynamic imaging model of infectious diseases was established to calculate the cumulative superimposed density of epidemic in 17 cities (prefectures). An evaluation rule of urban risk grade is established and evaluates the COVID-19 risk of 17 cities. The results show that (1) the higher the superimposed density of urban epidemic, the more infected people. (2) In the incubation stage, the thermodynamic imaging shows a point distribution, random walk, and outward diffusion trend. In the initial stage, the color of thermodynamic imaging gradually deepened and the range gradually expanded. During the burst stage, the thermodynamic imaging color deepens rapidly and the scope expands rapidly. In the stable stage, the thermodynamic imaging color becomes darkest and the range is extended to the pole. (3) According to the situation of COVID-19 transmission in Hubei Province, the cumulative superimposed density of Wuhan epidemic is far more than 10,000, ranking as “highest-risk.” Xiaogan and other 10 cities have a cumulative superimposed density within the range of [1000, 10,000], ranking as “high-risk.” Shiyan and other 5 cities have accumulated superimposed density values within the range of [100, 1000], ranking as “medium-risk.” Shennongjia cumulative superimposed density value is less than 100, and the level is “low-risk.”