The invention discloses a solid rocket engine heat insulating layer ablation rate testing method. The problem that the large solid rocket engine heat insulating layer ablation rate is difficult to measure is solved, and the invention belongs to the field of propellant heat insulating layer performance; a simple and easy small test solid engine is designed, and analogue simulation of the large engine heat insulating layer ablation state is achieved through ground tests; by controlling the small test solid engine airflow channel area, the mass flow of the small test solid engine airflow channelunit area is equal to the mass flow of the large engine unit area, simulation use of the designed small test solid engine device can relatively truly reflect the large solid rocket engine heat insulating layer ablation condition, and reference and guiding functions are provided for technology design persons for designing the large solid rocket engine heat insulating layer.