The thermostability of protein thermostable cathechol 2,3-dixoygenase (TC23O) has been studied by the parallel molecular dynamics simulations. By analysis of the exponent β, which is related to the scattering spectrum and constant-pressure heat capacity C_p, we reveal the respective contribution of a specific residue 228 proline; a specific salt bridge, Lys188N-Glu291OE1; four ions; and a different water environment to the thermostability of TC23O. The dynamic transition temperature of the mutants, Pro228Ser and Glu291Gly of the TC23O, was decreased about 10° C and 19° C respectively. The displacement of the four ions had no significant effect on the thermostability of TC23O. Water affects the thermostability by influencing the changes of accessible conformation to a certain extent. All these results agree with the known experimental results.