An armrest structure includes a main base tube, an outer base tube, a control member, and a spring, and the control member includes a pivot part, a press control part, a fastening part, and a restraining part, when the press control part of the control member is pressed, the spring is pushed to store elastic energy, and the fastening part of the control member can be released from being engaged with the main base tube, and the outer base tube can be adjusted to longitudinally lift; in the other hand, when the force applied on the press control part of the control member to press and buckle is removed, the fastening pan can be engaged with the main base tube, so that the outer base tube is unable to lift and move relative to the main base tube.