The utility model relates to a machine for automatically sealing a pressure-sensitive adhesive envelope, comprising a sample conveying mechanism, a positioning mechanism, an adhesive-applying mechanism, a composite mechanism and a cutting and sealing mechanism. The utility model is characterized in that the sample conveying mechanism is connected with the positioning mechanism through a chain; the positioning mechanism is connected with the composite mechanism through a belt; the composite mechanism is connected with the cutting and sealing mechanism through the belt. After connected with and a decelerator, a motor is connected with the cutting and sealing mechanism, the composite mechanism, the positioning mechanism and the sample conveying mechanism through a drive shaft and a gear. The utility model has the advantages of increased work efficiency and convenient and sanitary use, and can be sealed so long as protective strips are ripped away.