The invention relates to a method for fixing a filter cake in a bag type dust collector and aims to research the compression and resistance change rules of a filter cake layer in a process of trapping dust by using a dust bag. In the method, a small number of curing agents is added into the dust and aerial fog is introduced for fixing after the filter cake is formed on the surface of a filter material, so that the filter cake which has high mechanical intensity and is difficult to loosen can be obtained. Therefore, the preparation difficulty of a sample is lowered greatly when the structure of the surface or the cross section of the filter cake is observed and analyzed. The method is characterized in that: a fixing process has short time and a fixing method is simple; a fixed filter cake has high mechanical intensity and is difficult to loosen; and the structure of the surface or the cross section of the filter material can be analyzed by using equipment such as a microscope or a scanning electron microscope and the like, the structure of the filter cake can be actually reflected and a new method is provided for the research of the microstructure of the filter cake.