The radiators with different large height/width ratio mini-channels are designed for cooling high power density laser. Using deionized water as working fluid,it is found that the radiator with 3 mm height mini-channels can achieve heat dissipation of 3×106 W/m2 when surface temperature is 70 ℃ and flow rate is 58.2 L/h. The detailed experimental results show that the heat dissipating capacity is linearly with surface temperature for all mini-channel radiators when coolant flow rate is fixed. A suitable mini-channel height is required for maximum heat dissipation for this kind of radiator. A general empirical formula is proposed to evaluate cooling performance of the radiators with consideration of Nussel number (Nu) as a faction of Reynolds number (Re),height/width ratio,length/diameter ratio,and Prandtl number (Pr). Compared with the experimental data,it is found that the formula can describe heat dissipation performance of mini-channels radiator well. The average heat resistance of the radiator decreases with increasing of flow rate in mini-channels,while the trend is affected by the channel height. For maximum heat removal purpose,the mini-channels radiators have optimum working flow rate and channel height.