Using digital processing technique, a novel dither offset evaluation apparatus is designed for mechanical dithered ring laser gyro (MDRLG). Theoretical analysis shows that the dither offset can be obtained both from the absolute value and valid value of angle rate. The digital realizations of both the two apparatus are introduced in detail. Simulations of them show that both the two apparatus can evaluate the dither offset even when the dither amplitude and dither frequency changes. Using the real time dither offset as the dither amplitude reference can achieve a better dither driving stability than using the feedback of piezoelectric transducer.