A sputum suction tube adapter with switching function comprises a manifold, a switch module and a cover body. The manifold includes a main body and a pivoting part. The main body contains a base pipe and at least one joint pipe. The base pipe has an internal passage therein. The at least one joint pipe is fixedly connected with the base pipe of the main body and has a port which is communicating with the internal passage. The pivoting part is fixedly connected with the main body and provided with an opening communicated with the inner space. The switch module is rotatably connected with the pivoting part and comprises at least one communicating pipe. The at least one communicating pipe comprises a communicating hole selectably communicated with the internal passage. The cover body is covered to the pivoting part. The communication of the communicating hole with the internal passage is controlled by the rotatable switch module to connect the communicating pipe with the sputum suction tube for sucking sputum.