In laser thrusters, the reflectors of the focusing system work under high-intensity laser radiation. The material choice of the reflectors is quite important due to thermal load raised by laser absorption. Meanwhile the endurance of heavy thermal load should be attributed to the metallic reflectors with low laser energy absorption ratio. Based on two-dimension heat conduction equation and several approximations, this study investigates the melting time and thermal deformation characteristics for three kind of metallic materials that are of high heat specific heat, high conductivity and high melting point, and so are some alloys. Calculated through Finite Differential Method, the results show that, as for the twice reflecting focusing system, the thermal load is quite remarkable for the both reflectors and is more serious for the second one, while different materials present distinct thermal endurance performance. For the materials under study, the beryllium mirrors featuring higher specific heat could endure longer laser radiation and may prolong the work time. Moreover, if the reflecting mirror is required to work under high laser radiation for longer time, the aid of cooling system maybe indispensable.