Direct simulation Monte Carlo code is developed to study a catalytic process of atomic oxygen on thermal protection material surface. The present method employs the phenomenological electronic excitation model and the heterogeneous catalytic model. Numerical method is applied to simulate the flowfield around a test piece put into the rarefied dissociating oxygen test flow. The calculated number density ratio of oxygen to argon is compared with the measured emission intensity ratio of oxygen line to argon line. The sensitivity analysis is made by varying Eley-Rideal reaction cross section under the several conditions of collisional desorption cross section, sticking coefficient, and total number of surface site. It is found from the study that the probability value of Eley-Rideal reaction for the test piece made of a sintered silicon carbide is about 0.035, while the value of about 0.1 is deduced for the test piece made of copper.