Abstract: Through welding thermal simulation experiments, simulate the welding thermal cycle process of the coarse grain heat affected zone (CGHAZ) of 800 MPa grade steel for photovoltaic brackets under different cooling rates. Observe the microstructure of the thermal simulation sample under an optical microscope(OM) and analyze the influence of cooling rate on the microstructure of CGHAZ; The influence of cooling rate on the toughness of CGHAZ was analyzed by impact test of thermal simulation sample and scanning electron microscope(SEM). The results showed that with the increase of cooling rate, the microstructure of CGHAZ gradually changed from granular bainite(GB) and proeutectoid ferrite(PF) existing at grain boundary to GB and a small amount of lamellar bainite(LB), and finally to all LB. Moreover, with the increase of cooling rate, the impact toughness gradually improves, and the average impact energy gradually increases from 14.33 J to 58 J. The impact fracture morphology gradually changes from a typical brittle fracture morphology to a toughness and cleavage mixed fracture, and finally becomes a clear ductile fracture feature. In addition, considering the high strength of 800 MPa grade steel for photovoltaic brackets, its weldability is indirectly evaluated by the carbon equivalent and the Granville diagram, and its cold crack tendency is evaluated by the cold crack sensitivity index. The analysis results show that its weldability is good, and the welding cold crack tendency is small.