52 ml deflagration test apparatus is a closed vessel to evaluate characteristics of gas generating agents with small amount of the sample. An evaluation method of the linear burning rate of gas generating agents by fitting a simulated time - pressure curve to results of 52 ml deflagration test apparatus was established. The effect of heat loss was taken into consideration in this simulation. The time - pressure curves of experimental results with single base propellant were in agreement with simulated curves obtaind by input of almost the same value as references into the coefficient a and the exponent n. The linear burning rate of a gas generating agent can be evaluated with small amount of the sample by using this method.