The invention belongs to the technical field of optoelectronics and measurement, and particularly relates to a method and a device for measuring frequency stability of single-frequency pulse laser. The method includes taking a reference light source with high stability as a frequency standard, allowing the reference light source to generate certain frequency shift relative to a to-be-measured light beam, and beating with the to-be-measured light beam to acquire information of frequency stability of the to-be-measured single-frequency pulse laser according to frequency information of beat frequency signals. The device is simple in structure; the method utilizing the device has good real-time performance and high measurement precision, completes real-time measurement of frequency stability of the single-frequency pulse laser, and scientifically solves problems of high design difficulty in frequency stability measurement of the single-frequency pulse laser and high measurement error caused by shake of measuring systems.