Thermal bulk copolymerization of styrene (monomer 1) and maleic anhydride (monomer 2) was carried out in a continuous stirred tank reactor (CSTR) with a double helical ribbon-anchor impeller. A series of experimental runs under different operating conditions (average residence time, reaction temperature, and the composition in the inflow stream) were done, which showed that steady states could be approached. The effect of operating conditions on monomer conversion and copolymer composition was discussed. A CSTR model was established and the model parameters from the semicontinuous tests were used to predict conversions and copolymer compositions of the continuous process under transient and steady states. Kinetics from the semicontinuous bulk copolymerization were transferable to the continuous process. The modeling work for the continuous process showed that the same result as in a semicontinuous process could be obtained; the numerical method in which the gel effect on the copolymerization was incorporated exhibited excellent agreement between the model calculation and the experimental data. However, when using the assumption that k(22) = 0, k(21)[M-1] much greater than k(12)[M-2], (R-I/2k(t))(1/2) is a constant, and V is a constant, the predictions from the analytical solution to the model were in good agreement with the actual process data.