This paper investigated the cross-flow wet cooling tower, constructed the evaluating indicator on the basis of the heat and mass transfer performance, and then used classical four-variables model to study the effect of different seasons and ambient parameters (temperature, humidity and so on) on the heat and mass transfer of the cooling tower, and finally, gave the suitable operation condition of annual round operation in Nanjing, Wuhan and Chongqing. The results show that the suitable water-air ratio condition of CT is 0.5~1 in July and August of the three cities, and in June and September, 0.3~1. During transition season, the suitable water-air ratio condition of CT is 0.4~0.6, and the suitable operation time is March and November for Nanjing and Wuhan, but CT in Chongqing is not suitable for operation during the transitional seasons. In winter (from December to February), the suitable water-air ratio condition of CT is 0.5~0.76.