Abstract: OBJECTIVE To prepare the solid dispersion of efavirenz by spray drying with different grades(L, M, H) HPMCAS as the carrier, and the different dissolution models based on 3 grades of HPMCAS were preliminarily explored. METHODS The physicochemical properties of solid dispersion were characterized by X-ray powder diffraction(XRPD) and scanning electron microscope(SEM), the dissolution of solid dispersion with different drug loading ratios and different grades of HPMCAS was determined with dynamic solubility, the different dissolution models were determined by particle size analyzer and transmission electron microscope(TEM) and SEM. RESULTS XRPD analysis showed that efavirenz in the solid dispersion exhibited an amorphous form in HPMCAS. The morphology of efavirenz-HPMCAS observed by SEM exhibiting "shriveled raisin". Compared with 1:1.5, the solid dispersion with drug loading ratio of 1:6 displayed faster dissolution in pH 6.8 phosphate buffer solution. Furthermore, the solid dispersion of HPMCAS L dissolved faster at the same drug loading ratio. CONCLUSION Various dissolution models are determined in the solid dispersions with various grades of HPMCAS under pH 6.8 phosphate buffer solution. Efavirenz in the solid dispersion with HPMCAS L and M is dissolved in nanoparticles at the drug loading ratio of 1:6, while in 1:1.5, the drugs were released from the skeleton of carrier, similar to erosion dissolution model.