The invention discloses an air filling method based on paste filling. The method comprises the following steps that: 1, air bags are laid on the ground of a goaf, and then, a separating wall is installed for separating the space into a sealed filling space; 2, a material distributing pipe is arranged through a material pipe installing hole of the separating wall, and an air inflating pipe of each air bag is connected with a high-pressure air pump; 3, when the paste filling ground height reaches 20 to 30cm, the air bag is inflated, so that the paste filling and the air bag inflation are maintained to be synchronously performed; when the top surface filled with paste touches the top of the filling space, the paste filling is completed; and the air bag is continuously inflated until air pressure in the air bag reaches the pressure of overlying rock, the high-pressure air pump is closed, and the air filling is completed; and 4, the first step, the second step and the third step are repeated for performing a next round of filling. The air filling method has the advantages that on the basis of paste filling, an air filling process is added; the insufficient top filling quantity can be effectively reduced; the filling ratio is improved; filling materials are saved; and the supporting strength of a filling body is ensured.