The Re-entrant FiberOp tic Gyro (Re2FOG) is a new kind of FiberOp tic Gyro ( FOG) ,whichmakes the two counter-propagating lights re-enter the Sagnac Sensitive Ring( SSR). In this paper , a novel signal detection method for Re-FOG is presented. With the tow counter-propagating lights being modulated by a series of pulses, the interference signals of different number rounds of circling get different phase modulation. By thismethod of modulation, the signals of different number rounds of circling can be separated to get the rotation speed of the gyroscope. Signals of 1 round and 2 rounds of the gyroscope are experimentally separated , and the rotation speed of the gyroscope is detected. The experimental results show that the signal detection method is practical, and the bias stability of the Re2FOG is less than 4°/h.