In order to deeply understand the nitrogen excretion rules of marine cultured fish, precisely calculate the water exchange ratio (amount) needed, and provide basic data and technical support for the design of Deep Sea Aquaculture Farming Platform, TAN excretion rate of Oplegnathus punctatus under different feed frequencies was studied and the calculation method of water exchange ratio was analyzed. Results show that the ammonia excretion rate of Oplegnathus punctatus is (6.23±6.71)mg/(kg·h) under starved condition, (18.16±11.90)mg/(kg·h) when fed one time per day, (21.69±17.52)mg/(kg·h) when fed two times per day, and (17.98±12.93)mg/(kg·h) when fed three times per day. Based on the principle of mass balance, one kind of water exchange ratio calculation method is put forward for keeping TAN stable. By using the method, the water exchange ratio under 4 different conditions are 0.18, 0.55, 0.66, and 0.55 times/h, respectively. The verification test is under the condition of culture density 13.4 kg/m3, and the water exchange ratio is calculated as 1.09 times/h. Results show that TAN concentration can be maintained within the required level of the test design.