The application provides an annular air injection heat insulation parameter calculation method and device. The method comprises: calculating pressure field distribution of steam in an insulated pipe; calculating temperature field distribution of the steam in the insulated pipe according to the pressure field distribution of the steam in the insulated pipe; calculating dryness field distribution of the steam in the insulated pipe; calculating pressure field distribution and temperature field distribution of annular gas between a sleeve and the insulated pipe; determining a critical condition when the steam is mixed with the annular gas; and calculating a critical gas injection displacement of the annular gas according to the critical condition in combination with the pressure field distribution, the temperature field distribution and the dryness field distribution of the steam as well as the pressure field distribution and the temperature field distribution of the annular gas. The annular air injection heat insulation parameter calculation method and device provided by the embodiment of the application are capable of saving the heat insulation operation cost.