Component Cooling Water system and Essential Service Water system constitute the nuclear island cooling chain system of the China Pressurized Water Reactor 1000 Nuclear Power Plant. To deal with external events like aquatics and debris invasion, it is required that to expand flow channel of heat exchanger. This paper describes the basic structure of nuclear island cooling chain system, introduces the basic characteristics of CCW/ESW plate heat exchanger, obtains the empirical formula of capability of heat transfer plate by classical method, calculates and analyzes the effect of improvements by directly replacing heat exchanger and ESW pump. Study found that supply temperature of CCW must be raised, so that the improvement can meet the requirement of both the high seawater temperature and the depth of corrugated heat transfer plate. Combined with the calculation, raising supply temperature of CCW is the key step of improvement. The improvement of heat exchanger should be based on it. Before the improvement was applied, the nuclear power plants in high temperature sites should formulate the operation management measures firstly. Replacing ESW pump can only be considered as a last choice, for the limited effect, the high cost and the too long construction period.