The modification effect of β-cyclodextrin by dimethyl carbonate in the temperature range of 50℃ to 170℃ was systematically studied at atmospheric and high pressure respectively, using dimethyl carbonate as green modification reagent and anhydrous potassium carbonate as alkaline catalyst in N, N-dimethylformamide. The products were purified through preparative HPLC, and characterized by means of IR, ESI-MS, 1HNMR and 13CNMR. The results showed that methoxycarbonylation derivatives with low degree of substitution were prepared in the temperature range of 50℃ to 85℃, and the major compound was mono-methoxycarbonyl-β-cyclodextrin, of which the yield reached 60.91%; the methylation and methoxycarbonylation of β-cyclodextrin occurred simultaneously in the range of 90℃ to 140℃; while when operating at the temperature from 160℃ to 170℃, and the pressure of approximately 1.40 MPa, randomly methylated β-cyclodextrins with the substitution degree range of 7 to 9 were obtained with a high yield from 80% to 85%.