In the photovoltaic field, LED has been proven to be a promising artificial light source, and its spectrum can synthesize sunlight spectrum. At present, the key problem of synthesizing the sunlight spectrum through different kinds of LEDs is how to select led models from the LED database and determine the working parameters of each model of LED. To solve this problem, scientists have proposed various mathematical spectral models to express the spectral power distribution of LED, such as the Gaussian function, Lorentz function, logistic power peak function and so on. These mathematical models can accurately reflect the nonlinear spectral characteristics of LED, including peak wavelength, FWHM, redshift and so on. However, the LED spectrum simulated by the mathematical spectrum model is different from the real led spectrum. The LED spectrum curve simulated by the mathematical spectrum model is symmetrical. However, the spectral curves of real blue and green LEDs are steeper on the short wavelength side and slower on the long wavelength side, while the spectral curves of red LEDs are the opposite. Based on the existing LED light sources, this paper proposes a new method to simulate the solar spectrum. The simulation experiment is carried out by designing a filter and adjusting the radiation weight of each existing LED light source (the radiation weight of an LED light source is the percentage of the radiation of the current LED light source and the maximum radiation of the LED), to simulate a new light source and make its spectrum close to the sunlight spectrum. That is, one filter is placed under the mixed light source of multiple LEDs, and the spectrum of the light source is limited by the spectral transmittance of the filter and the radiation weight of each LED light source so that the spectrum of the modified multiple LED mixed light sources is as close to the spectrum of the daylight light source as possible. Due to industrial requirements, it is necessary to smooth and constrain the spectral transmittance curve of the filter. Finally, through the spectral transmittance of the optimized filter, the least square solution of the radiation weight of each LED light source is obtained to obtain the radiation weight of each optimal LED light source. Through the simulation experiment, the correlated color temperature (CCT) of the simulated sunlight light source obtained by this method is 6 492, and the correlated color temperature of the target light source is 6 503. The correlation index (R2) between the simulated sunlight source and the sunlight spectrum is 0.992 6. The method of this paper provides an important reference value for the research of solar spectrum fitting based on LED.