Safe, efficient and flexible indirect air cooling high-back-pressure heat supply system and heat supply method

The invention discloses a safe, efficient and flexible indirect air cooling high-back-pressure heat supply system and a heat supply method. The heat supply system comprises an indirect air cooling system, two heat supply network initial stations, a first front condenser, a second front condenser and a steam increasing machine, wherein the indirect air cooling system is composed of two machines and one tower, and the three towers are integrated. Dead steam in the steam turbine is divided into two paths after entering the main condenser, one path enters the first front condenser, the other path sequentially enters the steam increasing machine and the second front condenser, the first front condenser and the second front condenser conduct gradient heating on heat supply network return water in the heat supply network system, and the heat supply network return water subjected to gradient heating enters two heat supply network initial stations; and the high-pressure steam output by the steam turbine is used for fu