Abstract: During last decades, TPDmethod is used for determining heat of desorption of the gases adsorbed on the surface of solid catalyst and for testing state of the gases adsorbed. Even now the method is used in the thermal decomposition reaction. Generally, re-adsorption is ignored in treatment of TPDexperiment data. In the same appraximation condition, it is convenient to calculate the coverage θ if we let (1+βt/T₀)¹ = 1-βt/T₀, where t is the time of reaction, β is the rate of raising temperaiure, and T₀ is the temperature where t = 0.