Based on a drift current model, along the channel current of MM20 model, an approved SOI LDMOS compact model is presented in this paper. A continued and concise expression of the presented model for easily analysis of harmonic balance, which considers the quasi-saturation effect of SOI LDMOS and short channel effect, are observed. Comparison of simulated results of DC I-V and transform characteristic for the presented model with measured data are made, which shows they are well agreed, and this model is verified.