In order to overcome the shortcomings of the existing methods for measuring plume velocity produced by solid rocket motor propellant combustion, a tunable diode laser absorption spectroscopy (TDLAS) technique was proposed to measure plume velocity. By measuring the characteristics of a single absorption line of hydrogen peroxide molecule in combustion products at 1 392 nm, the spectral frequency shift and molecular velocity were established according to Doppler effect. The relationship was used to obtain the airflow velocity, which solved the problem that the contact measurement method could interfere with the plume flow field and the inhomogeneity of tracer particles in the traditional non-contact measurement, and the effective experimental data are obtained. Futhermore, through the analysis and processing of the experimental data, the plume flow velocity of the engine was obtained.