A height measuring includes a mounting base, a measuring mechanism, and a controller. The measuring mechanism includes a driving member, a measuring member, and a sensor. The driving member is mounted onto the mounting base. The sensor is positioned on the driving member. The measuring member is movably positioned on the driving member and passes through the sensor. The driving member is configured to drive the measuring member to move until it contacts a workpiece in a jig. The controller is electrically connected to the sensor and prestores a moving distance range. The sensor is configured to sense a moving distance of the measuring member and transmit the moving distance to the controller. The controller is configured to judge whether or not the workpiece reaches a proper height relative to the jig by comparing the moving distance data with the prestored distance range.