The invention discloses a device and method for eliminating residual circular polarization components in linearly polarized light angle detection. The device and method are based on photoelastic polarization modulation technology, light polarization compensation technology and digital phase-locking amplification technology. A photoelectric detector and phase-locking amplifier obtain the first harmonic component of a polarization modulation detection output signal. By using the response characteristics of alkali metal atoms to a magnetic field perpendicular to the detection light direction, the optical-axis azimuth angle of a quarter wave plate is adjusted finely to precisely compensate a light polarization state, thereby eliminating a caused polarization error signal. A compensation process can be monitored by digital oscilloscope in real time. The device and method not only used in high-sensitive atomic magnetic field/inertia high-precision signal detection, but is also suitable for high-precision weak-light angle measurement.