A simple method used for simultaneous measurement of phase retardation and optic axis of wave plate by employing 1/4 wave plate is demonstrated. The theoretical analysis of the measuring principle is presented in detail. In the measurement,after adjusting a standard 1/4 wave plate and the fast (slow) axis of the plate to be measured parallel to the pass axis of the polarizer,the plate to be measured is rotated by 450 counterclockwisly. A stepping motor is used to rotate the analyzer. The experimental data are collected by a photodetector and then sent to a computer. According to the output data curve,the phase retardation and optic axis of the plate to be measured can be obtained simultaneously. To test the feasibility of the method,a λ/2 and a λ/8 wave plates are used as examples to demonstrate the measurement procedures. The phase retardation measurement accuracy is better than 0.5 × 10-2. This method can be used to measure the arbitrary phase retardation conveniently.