Light propagation in nanoparticle-loaded encapsulants is simulated based on the method of Monte Carlo, referring to the multilayer graded refractive index structure for LED encapsulants. And the influence of scattering coefficient on transmittance is analyzed. The results show that the transmittance decreases with scattering coefficient. For a given number of layers, the encapsulants will yield maximum transmittance if the refractive index value of each layer is optimized. The nanoparticle-loaded encapsulant consists of multiple layers with refractive-index values that gradually decrease, transmittance will be higher than in traditional non-graded encapsulants, and will improve light extraction efficiency of LED.