Abstract: A charge sharing physical model for the threshold voltage analysis in short-channel SOI BJMOSFET has been proposed,and the different threshold voltage complexions when the back interface were at accumulated,reverse-style and full-depleted state have been discussed detailedly.Then,the software Mathematica has simulated the characteristic curve of its threshold voltage.From our theoretical analysis and computer simulation,it can be seen that the threshold voltage in short-channel SOI BJMOSFET can be controlled easily and it will be more fit for the request of modern LUSI to low voltage and low consumption.