The single longitudinal mode(SLM) passively Q-switched smooth pulse laser is widely used in the fields of precision measurement,optical communications,high-resolution spectroscopy and so on.Its frequency stability directly affects the accuracy of measurement results.In this paper,we propose a measurement method of the frequency stability of SLM passively Q-switched laser based on the pulse waveform observation,interference fringes imaging and scanning angle of light intensity.Firstly,we establish the experi...