Aiming at the requirements of efficient heat dissipation and uniform cooling for high heat flux laser medium, an experimental platform of open single nozzle spray was designed and established by using the deionized water as cooling medium. The spray cooling heat transfer coefficients and cooling uniformity effect in the single-phase region were obtained at different heat flux (16～110 W/cm²), flow rates (200～300 mL/min) and spray heights (15～25 mm). It is concluded from the experimental results that the cooling efficiency and temperature uniformity were significantly affected by the spray height and flow rate under different heat flux. The maximal heat transfer coefficient of 5.93 W/(cm²·K) was got at the spray height of 15 mm and flow rate of 200 mL/min, while the temperature uniformity could be greater than 0.6 ℃ with the heating area of 20 mm×20 mm at the spray height of 15 mm and flow rate of 250 mL/min.