A simple but reliable measurement method for the dynamic phase shift in a passive homodyne interferometric fiber-optic sensor is proposed. The amplitude of the dynamic phase shift is calculated directly from the photodetector output. A Mach-Zehnder interferometer with a PZT, which is used to generate the simulation signal, is constructed. The experimental results obtained using this simple method are well in agreement with the results given by the standard phase generated carrier (PGC) method, which shows the validity of the results. This new method has the advantages of simplicity of operation, no active element in the sensing head, no modulation to the laser, large dynamic range and working bandwidth, etc. It can be used for the dynamic phase shift measurement of various interferometric fiber-optic sensors.