The utility model relates to a water quality adjusting and mixing device for ship desalted water. The device comprises n PH regulation dosing tanks and n metering pumps, the device further comprises nmixers, a pH sensor, a TDS sensor and a PLC, n mixers are connected in series between the treated water inlet and the quenched and tempered fresh water outlet through a treatment water pipeline; theith hardening and tempering agent flows out of the ith PH adjusting and dosing tank, is pressurized and conveyed to a treated water pipeline through the ith metering pump, enters the ith mixer to be fully mixed and dissolved with treated water and then is output to enter the next mixer; wherein the pH sensor and the TDS sensor are installed in front of a fresh water outlet subjected to hardening and tempering treatment, the pH sensor and the TDS sensor collect a water pH value and a water hardness value and send the water pH value and the water hardness value into the PLC, the PLC outputs a control signal for adjusting the feeding amount of each hardening and tempering agent to each corresponding metering pump, and i is equal to 1, 2,..., n. And the purposes that the tempering agents do not react with each other to form precipitates and the content of the effluent tempering agent is stably tested can be effectively achieved.