In order to achieve a LEDbased solar simulator or a standard spectrum lamp with high stability and good spectral matching that can be used in measurement, a method is proposed to accurately simulate the spectral power distribution (SPD) of AM1.5 by adopting many different peak wavelength LEDs. Least square (LS) method and the characteristics of Gaussian distribution are considered during the process of simulation. This approach theoretically achieves a spectral synthesize in order to guide the LED types selection and the drive current value. Experimental result proves its feasibility and show that: in the range of 300~1 100 nm, the spectral mismatch error is less than ±2.76%, and less LED species are adopted. This algorithm can accurately distinguish the absorption valleys of standard solar spectrum AM1.5. When applied to AM0, it results in the spectral mismatch less than ± 1.67%. For engineering application, the algorithm gives a good guiding significance to access standard solar spectrum lamp.