The invention provides a method for locking an interference phase difference of an optical field. The method comprises the following steps of: adding/subtracting a direct current signal output by a photoelectric detector to/from a differential signal which is output by a mixer and has a sine mode to acquire an error signal capable of locking any interference phase difference of the optical field; and feeding the acquired error signal back to piezoelectric ceramics in an optical path through a proportional integral controller and a high-voltage amplifier to lock the any interference phase difference of the optical field. The invention also provides a device for realizing the method for locking the interference phase difference of the optical field. The device can be used for coupling two optical fields at any phase difference, and can also be used for measuring the quantum fluctuation of orthogonal components in the optical field at any angle to optimize a quantum logic operation result and a quantum calculation result.