Many researchers from scientific and industrial fields have devoted their efforts to the laser interferometer, aiming to improve the measurement accuracy and extend the practical applications. Here, we present a modified homodyne laser interferometer based on phase modulation for simultaneously measuring displacement and angle. The active sawtooth wave phase modulation enhances immunity of this interferometer to the environmental fluctuations and laser power drift. Based on polarized optic theory and the sinusoidal measurement retro-reflector, a modified Michelson-type interferometer configuration is designed to simultaneously measure displacement and angle. Phase difference between the reference and measurement interference signals can be obtained using the sawtooth wave phase modulation and zero crossing detection technique, where the real-time displacement and angle values can be derived directly. Experimental results demonstrate our proposed interferometer has good static and dynamic performance.