The correlations between the internal and the process variables in plasma etching were derived based on fundamental theories as well as experimental data from literatures. The rates of plasma etching in SF₆ system were calculated based on these correlations, which agreed with the reported experimental values within the same orders of magnitude. The etch rates calculated for various process conditions changed in the same trend as the experimentally measured ones. Reactive ion etching(RIE) in Cl₂/HBr/He system was performed under different pressures and electrical powers. Parameters in the correlation equations derived from literatures were replaced by three adjustable parameters, C₁,C₂ and C₃, which were determined by fitting the simulation profiles to the three experimental results. Trench contours simulated using these parameters agreed well with those obtained from the experiments.