Method for raising recovery efficiency of heavy oil deposit through chemical steam flooding

The invention provides a method for raising the recovery efficiency of a heavy oil deposit through chemical steam flooding. The method comprises steps of: 1. selecting an oil deposit and injecting steam, wherein the burial depth of an oil layer of the selected oil deposit is 900 to 1600 m, the effective thickness of the oil layer is greater than or equal to 8 m, the viscosity of crude in the oil layer is greater than 100 mPa.s, and the volume of the injected steam is 0.2 to 0.25 times of that of pores in the stratum; 2. injecting a foaming agent, nitrogen and steam in a steam injection well in a mixed mode for 10 to 30 days, wherein the ratio of the injected foaming agent to the injected steam, by mass, is equal to (0.4 to 1.2) to 100, and the ratio of the injected nitrogen to the injected steam, by volume underground, is equal to (0.5 to 1.5) to 100; 3. injecting an oil displacement agent and steam in the steam injection well in a mixed mode for 5 to 10 days, wherein the ratio of the oil displacement agent to the injected steam, by mass, is equal to (0.2 to 0.8) to 100; 4. only injecting steam for 80 to 120 days; and 5. repeating steps 2, 3 and 4. The speed of steam injection is 1.6 to 2.0 ton/day, hectare, thickness per meter.