The invention discloses a cubesat magnetometer expanding mechanism which comprises an end cover, a box body, a connecting rod, fixed hinges, rotary hinges, locking sheets, a rotary shaft, a locking rod and a torsion spring. When not working, the cubesat magnetometer expanding mechanism is attached to the surface of a satellite through a burning line system. After the cubesat magnetometer expanding mechanism is lifted off, the burning line system works, a burning line is burnt out, and the restraint on a magnetometer is released. Under the effect of the torsion spring, the rotary hinges drive the connecting rod and the box body to pop up and when the connecting rod and the box body pop up to the position at 90 degrees, the central axis of a blind hole coincides with that of a through hole, the spring pushes the locking rod to pop up, and the cubesat magnetometer expanding mechanism is locked. By the adoption of the cubesat magnetometer expanding mechanism, the magnetometer is expanded to a target at the outer portion of a satellite body, and the influences on the magnetometer by the magnetic field in the satellite body can be effectively isolated.