The invention discloses a square sleeve-type actuator made of a shape memory alloy for increasing displacement, which relates to an actuator. The invention aims at the problem that the work space is restricted due to the oversize volume and incompact structure because a cooling or heating device of the current actuator made of the shape memory alloy is separated from the actuator. One end of a shape memory alloy wire in a middle layer is fixedly connected with a first head of an inner cylinder; the other end of the shape memory alloy wire in the middle layer is reversed at least once by a group of reversing pin shafts fixed on a second head of the inner cylinder, passes through the first head of the inner cylinder, is reversed by the first head of the inner cylinder, and then is fixedly connected with a first head of an outer cylinder; one end of a shape memory alloy wire in each outer layer is connected with a second head of the inner cylinder; and the other end of the shape memory alloy wire in each outer layer is reversed at least once by a reversing pin shaft fixed on the first head of the inner cylinder, passes through the second head of the inner cylinder, then passes through a second reversing column of the inner cylinder, and is verticality and fixedly connected with a second head of the outer cylinder. The actuator is used for outputting straight-line displacement andforce.