Considering　of　orbital　environments　and　working　mode　of　the　reflectors,　thermal　model　of　the　45-degree　reflector　assembly　in　satellite　optical　terminals　on　orbit　is　established　to　obtain　temperature　distribution　of　the　reflectors(the　extreme　low　temperature　is　-38.0　degrees　C,　the　extreme　high　temperature　is　32.2　degrees　C　and　the　max　temperature　gradient　is　3.3　degrees　C),　meanwhile,　a　thermal-optical　vacuum　experiment　based　on　the　analysis　results　is　conducted　to　check　the　effect　of　temperature　distribution　on　reflectors.　the　results　shows:　if　temperature　of　the　reflector　is　＞=-10　degrees　C,　the　reflector　shape　accuracy　PV　will　be　better　than　lambda/3,　and　the　RMS　will　be　better　than　lambda/30　(lambda=　632.8nm),　but　it　becomes　worse　and　is　not　able　to　meet　application　requirement　when　the　temperature　decreases　continuously(-40　degrees　C　similar　to-10　degrees　C).　So　it　is　necessary　to　design　reasonable　active　heating　loops　for　reflector　assembly　to　guarantee　its　performance　on　orbit.