Numerical simulation is carried out for the collimating and focusing lens of the 10 kW expanded beam fiber connector under different cooling modes and different parameters. The coupling lens size parameters （diameter of 40 mm to 60 mm and edge thickness of 5 mm to 25 mm） are obtained by using the ZEMAX simulation design. The thermal distribution of the lens is simulated by COMSOL Multiphysics to obtain the maximum surface temperature of the lens using the cooling method and the influence of lens size on temperature under different output powers using this cooling method. The simulation analysis of 20 sets of aspherical lenses with different size parameters but the same optical performance shows that when the power is above 20 kW, the lens can be cooled by side air cooling mode, the wind speed is 9 m/s, the lens diameter is greater than 50 mm, and the thickness is less than or equal to 5 mm. When the power is greater than 7 kW, the lens can be cooled by plane air cooling, the wind speed is 5 m/s, the lens diameter is greater than 30 mm, and the thickness is less than or equal to 5 mm. When the power is lower than 7 kW, the lens can be cooled by edge water cooling, the water flow rate is 1 m/s, and the lens thickness is less than 7 mm.