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 the 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. The transmittance will be higher than that of traditional non-graded encapsulants, and will improve light extraction efficiency of LED.