The 1064nm infrared laser plume measuring system is developed to evaluate the performance of solid propellant. In the paper the laser transmittance which the infrared laser permeats plumes exhausted by solid－propellant motor is analyzed and a dynamic measuringmethod with double lamphouse is suggested. The princip le of photoelectric measurement and the structure of the 1064nm laser plumes transmittance measuring system is introduced. The measuring error is less than 1% by experiment demarcating. The repeatability and precision met the demand of research on solid－propellantwith low characteristic signal.