1. A shift control system of a hybrid vehicle with an automatic transmission, comprising: a fuzzy function calculator that receives an accel position sensor (APS) signal that is an input variable, and outputs a severity value by determining a driver's driving severity value through a plurality of fuzzy rules including a fuzzy function for the APS signal; a sporty degree calculator that is electrically connected with the fuzzy function calculator and determines a sporty degree corresponding to the severity value; and a mode determiner that is electrically connected with the sporty degree calculator and determines whether an engine operates in accordance with the sporty degree.