A method to simulate the energy distribution of excimer laser is provided. The color image of an actual excimer laser energy distribution is captured, and the image and extract relevant information are analyzed using Matlab software. Meanwhile the actual excimer laser light source is simulated by the optical software Zemax. The beam dimension of the actual excimer laser light source is about 16.5 mm×35.4 mm. The beam divergence is about 3.3 mrad in the x direction, and 11.5 mrad in the y direction. The beam dimension of the light source simulated by this method is about 16.7 mm×35.3 mm, and the beam divergence is about 3.41 mrad in the x direction, and 11.53 mrad in the y direction. The energy distribution of the simulated light is consistent with that of the actual excimer laser light in details. This method provides a perfect solution to the optical simulation difficulty of the complex spatial energy distribution of the excimer laser. It also provides a technical foundation for the investigation on the optical property of excimer laser and development of its optical components.