The invention discloses a water quality source treatment system for a drinking water tank, which comprises a drinking water tank (1), a drinking water circulating pump (2), a control system (3), a dosing device (4), a cooler (5) and a temperature sensor (10). The inlet of the drinking water circulating pump (2) is connected with a first stop valve (11) and a second stop valve (12), and the outlet of the drinking water circulating pump (2) is connected with a first stop check valve (13) and a pipeline (8); the inlet of the cooler (5) is provided with a first magnetic valve (6), the outlet of the cooler (5) is provided with a second stop check valve (14), and the cooler (5) is provided with a by-pass pipeline (9); the by-pass pipeline (9) is provided with a second magnetic valve (7); the outlet and the inlet of the dosing device (4) are connected with the pipeline (8) respectively; the temperature sensor (10) is arranged above the drinking water tank (1); the control system (3) is connected with the drinking water circulating pump (2), the temperature sensor (10), the first magnetic valve (6), the second magnetic valve (7) and the dosing device (4) through cables. The water quality source treatment system disclosed by the invention ensures water quality safety from the water source and effectively prevents the breeding of organisms; has the advantages of high automation degree, safety and reliability; can meet the higher requirements of a shipowner on drinking water quality.