A large-angle sloping roof steel structure connected to a main body structure, including: an intermediate platform, inclined main supporting steel columns circumferentially connected at four corners of the intermediate platform, constructing steel columns and wind-proof surrounding beam connected between top ends of the inclined main supporting steel columns, where roof purlin are connected between the adjacent inclined main supporting steel columns at intervals. The invention provides a top-down inverted construction method for a large-angle sloping roof with a steel structure as the main structural form. By using the method, the operation safety of an inclined main stressed vertical member during the installation process can be ensured, and the investment of supporting measures is reduced by preferentially installing the intermediate platform, thus effectively ensuring the installation progress, quality and safety of the sloping roof steel structure. The present invention can be widely applied to sloping roof construction.