The invention provides a construction method of a steel structure heat-insulating water-proofing inverted accessible roof and relates to a construction method of roofs; the construction sequence is that: a net frame rod piece, a steel ball, a profiled bar, a bracket and a roof steel plate are manufactured; assembly and installation of the net frame are carried out; the installation of the bracketof the net frame is carried out; the installation of a steel girder is carried out; the installation of the steel plate is carried out; the installation of a water fountain is carried out; a cement ceramsite sloping layer, a cement mortar screeding layer and an APP modified asphalt water-proofing layer are constructed; a heat-insulating layer is constructed; an oil asphalt felt separating layer is constructed; a surface layer is constructed; and indoor fire-resistant coating for a steel structure is constructed. The construction method can form a space roof system which has the advantages of heat insulation, prolonging the service life of the water-proofing layer, energy-saving, environmental protection and accessibility, and the accessible roof has characteristics of long spanning, long column grid distance and large bay by systematically combining a reinforced concrete main structure.