The invention provides a method and equipment for preparing ketene by virtue of triode-type cascade reaction. Raw materials are pumped into a mixing tank so as to be mixed, then a catalyst is added, and the mixture is transferred to a vaporizer so as to be vaporized and then enters into a primary reactor, wherein a reactor pipe of the primary reactor has the length of 2.5m, a temperature of 700 DEG C and a pressure of 1MPa; the material discharged from the upper part of the primary reactor enters into a secondary reactor, wherein a reactor pipe of the secondary reactor has the length of 2.0m, a temperature of 750 DEG C and a pressure of 1.5Mpa; the material discharged from the upper part of the secondary reactor enters into a tertiary reactor, wherein a reactor pipe of the tertiary reactor has the length of 1.5m, a temperature of 800 DEG C and a pressure of 2Mpa; a buffer tank is evacuated, the material discharged from the rear upper part of the tertiary reactor enters the buffer tank after being condensed, and a product is discharged from the bottom of the buffer tank. During the tertiary reaction process, due to overhigh pressure, the gas released by a control system is discharged to the buffer tank after being condensed; the pipe length of the tertiary reactor can be scaled up in equal proportion. By adopting the method and the equipment, the conversion rate is above 96%, carbon deposition is avoided, blockage is prevented, and the safety is ensured.