The invention provides a spare pressure type heptafluoropropane fire extinguishing system. The spare pressure type heptafluoropropane fire extinguishing system comprises a power gas cylinder set, a driving gas cylinder set, a heptafluoropropane storage cylinder, a fire extinguishing agent container valve, a pressure reducing device, a power gas container valve, a driving gas container valve, a first starter, a second starter and an electromagnetic starter. When a fire breaks out, the electromagnetic starter and the gas driving cylinder set act, released gas enters the first starter and the third starter respectively, the power gas container valve and a selection valve are opened, and gas released from the power gas cylinder set constantly enters the heptafluoropropane storage cylinder after being subjected to pressure reduction by virtue of the pressure reducing device and delayed; and when pressure of a fire extinguishing agent in the heptafluoropropane storage cylinder reaches a certain pressure, the fire extinguishing agent enters the second starter by virtue of a connecting pipe, the second starter acts to open the fire extinguishing agent container valve, and the fire extinguishing agent in the heptafluoropropane storage cylinder extinguishes a fire in a specified protection zone by virtue of a pipe network. By applying the spare pressure type heptafluoropropane fire extinguishing system provided by the invention, safety of the fire extinguishing system can be guaranteed, and constant pressure stable output of heptafluoropropane also can be guaranteed.