In this paper, a new method of measuring complex piezoelectric constants ofpiezoelectric materials with Michelson interfermeter is presented.The interferometerconsists of two mirrors, one is allached to the sample and the other to the controlledpiezoelectric ceramic, By using photodiode and two phase, lock-in amplifier, theinterference figure is transfered, amplified and measured. A change of sample length dueto converse piezoelectric effect as small as 0.6 pm is detected. In the range of frequence of 2.5 Hz~2.5 kHz and temperature of -60~90 ℃, the d′31, d″31 of PEX5 piezoelectric ceramic of PZT series are measured and discussed.