Based on the mechanism of heat transfer，a one-dimensional finite difference model describing combustion process and array heat transfer of chemical microthruster was established. With this model，the temperature growth process and temperature distribution of unit wall of epoxy resin，7740# glass，microcrystal glass and silicon units filled with lead styphnate were obtained by numerical simulation. Results show that heat conductivity and combustion time of microthruster unit are the main factors affecting growth of temperature and integration level. Larger heat conductivity and longer combustion time lead to less microthruster unit on a same area. When heat conductivity increases by 100-1000 times，critical distance increases by 3.3-3.6 times，and when combusion time increases by 1 time，critical distance increases by 3-5 times. And critical distance is limited only in micron-size: silicon unit is 150-450 μm，and the other three types are 20-160 μm.