YAG:Ce3+ yellow phosphor are particularly used luminescent materials to produce white light in phosphor-converted white LED (pc-WLED). Surface coating of YAG phosphor is the main concern for desired optical performance of the phosphors. Many scholars conducted various experimental analysis on the surface coating of phosphors to improve yellow emission, but the theoretical explanation by which phosphor coating could help improving light efficiency has not yet been studied. In this paper, based on Mie theory, the optical constants such as scattering coefficient, absorption coefficient and asymmetry parameter of YAG:Ce3+ phosphor and YAG@SiO2 (YAG:Ce3+ phosphor surface coated with nano-SiO2 layer) were calculated. An optical configuration of chip scale packages (CSP) WLED was constructed by coupling YAG:Ce3+ or YAG@SiO2 phosphors with a LED laser. Based on the optical parameters calculated by Mie theory, the luminescent properties of YAG:Ce3+ and YAG@SiO2 WLED were simulated by Monte Carlo method. The results showed that a thin SiO2 coating layer on YAG phosphor result in an overall increase in luminous performances compared with original YAG WLED. The absorption coefficient of phosphor is the main concern affecting the light emission in WLED. Due to the fact that YAG@SiO2 possess higher 460 nm absorption coefficient , it could absorb more blue light than YAG, thereby it has a 1.2% higher conversion efficiency than YAG, finally the enhanced luminous efficiency of YAG@SiO2 WLED is obtained. The results obtained in this work provides a potential method in future WLED packaging designing.