The invention provides a method for loading and unloading a substrate in a cavity. The method comprises the following steps of loading and unloading, wherein the loading step comprises the steps of S1, at least opening a control valve of a back blowing passage, nearest to a based, on a back flowing gas path along an airflow direction so that at least one part of suppressed gas in the back blowinggas path is released to the cavity along the back blowing path of the base; S2, placing and fixing the substrate on the base; and S3, opening the back blowing gas path, and opening an air source so that the air source is used for supplying air to a back surface of the substrate through the back blowing gas path and the back blowing passage. The instantaneous pressure of air introduction can be reduced during back blowing on the substrate, so that the problem of substrate position deviation caused by excessively large instantaneous pressure of air introduction can be solved.