The invention belongs to the technical field of optics, and relates to a measuring device and method, in particular to a device and method for measuring the signal-to-noise ratio based on a single pulse for generating a pulse sequence. The device comprises a beam splitter, a double-sided reflection mirror, a reflection mirror, a first sum-frequency crystal, a second sum-frequency crystal, a dichroscope, a lambda/2 half-wave plate, a lens, a stepping motor and a detector CCD. The measured single pulse obtains the curve that the strength of the third harmonic pulse sequence changes along with retardation through the elements, and the signal-to-noise ratio of the measured single pulse is calculated through the curve. The method is simple in principle, the device is compact in structure, debugging is easy, and measurement precision is high.