3-dimensional numerical analysis for a rectangular magnetron cathode model is done to predict cooling characteristics of high power sputtering system for ZnO deposition. It includes cooling channel design, heat transfer analysis of a target, bonding layer and backing plate. In order to model erosion profiles of a target, ion current density distribution from 3D Monte Carlo simulation is used to distribute total sputtering power to 5 discrete regions. At 3 kW of sputtering power and cooling water flow of 1 liter/min at $10^{circ}C$, the maximum surface temperature was $45.8^{circ}C$ for a flat new target and $156^{circ}C$ for a target eroded by 1/3 of its thickness, respectively.