The objective of this research was to study the occurrence and seasonal variations of disinfection by-products (DBPs), including traditional carbonaceous and emerging nitrogenous DBPs, in a full-scale drinking water treatment plant (DWTP) for nearly 2 years. The removal efficiencies of each DBP through the treatment processes were also investigated. This DWTP takes raw water from the Yangtze River in East China. The quality of the raw water used in this DWTP varied with different seasons. The results suggested that DBP concentrations of the finished water were higher in spring (82.33 ± 15.12 μg/L) and summer (117.29 ± 9.94 μg/L) with higher dissolved organic carbon (DOC) levels, but lower in autumn (41.10 ± 5.82 μg/L) and winter (78.47 ± 2.74 μg/L) with lower DOC levels. Due to the increase of bromide concentration in spring and winter, more toxic brominated DBPs increased obviously and took up a greater proportion. In this DWTP, DBP concentrations increased dramatically after pre-chlorination, especially in summer. It is noteworthy that the removal of DBPs during the subsequent treatment was more obvious in spring than in the other three seasons because the pH value is more beneficial to coagulation in spring.