The hydrogen thermal desorption of a martensitic steel has been simulated assuming lattice hydrogen diffusion under a local equilibrium with reversibly trapped hydrogen as the rate-determining process. The calculated desorption curves reproduced the observed shift of the peak temperature associated with the specimen thickness and the heating rate. The calculation method involves a combination of a defect density and a hydrogen/defect binding energy as parameters. The dependence of the peak temperature on the defect density and the binding energy has been quantitatively shown. Assignment of the lattice defect relevant to the desorption curves is discussed. A calculation that took into account the increase in the defect density yielded results consistent with the observed change in the desorption curves associated with plastic strain.