The invention provides a construction method of an overhanging awning. The method comprises the following steps: S1, performing pre-embedded construction of sill anchors; S2, hoisting stiff steel columns; S3, dividing hoisting of roof main trusses into twenty four mounting units; S4, performing supporting mounting of a first section of a main truss; S5, firstly constructing a hoisting section I when a section of a main truss GHJ1 is mounted; S6, hosting an inclined stand column, hoisting the other end through a crane, and then hoisting a front end hoisting section II or the next main truss; S7, performing supporting mounting and main truss mounting according to the steps S4 to S6, so as to form a first mounting unit; S8, tying rods between two main trusses and mounting secondary trusses, and adopting high-altitude connection for a secondary truss between each two main trusses; S9, accomplishing the other twenty three mounting uses through circulation of the steps S4 to S7. The method solves the problems of large span of trusses, long components and high construction difficulty during the construction of the traditional overhanging awning by mounting the trusses section by section in a region, meanwhile increases temporary supports, and improves the lateral stability of single truss.