Using water as coolant, Steinen 1.5, 2.0 full-cone nozzles with spray cone angle 60° were applied to study heat transfer performance of spray cooling for high-power laser in non-boiling regime when mass flow rates ranged from 3.26 L/h to 5.0 L/h. The results indicate that heat transfer can not be judged by mass flow rates only. For the same nozzle, the increasing of pressure and mass flow rates resulte in the increasing of heat trarsfer performance. For different nozzles, the heat transfer performance doesn′t increase obvirously, if droplet velocity is not varied significantly, increased mass flow rates can change other spray parameters such as droplet flux, droplet size and film thickness, and all the parameters determine spray heat transfer performance together. Mass flow rates and droplet velocity are the key parameters to influence cooling efficiency. For the same nozzle, enhanced pressure could result in cooling efficiency drop. Compared with smooth wall, the rough wall has better heat transfer performance and cooling efficiency in non-boiling region.