This paper presents a novel two-layer and two-loop spatial deployable linkage which can only accurately output vertical straight-line motion. First, the degree of freedom (DOF) of the linkage is analyzed based on structure decomposition and screw theory, and the characteristic of the straight-line motion of the linkage is verified by checking the output twist of the end platform. Then, the kinematic model of the mechanism is established based on the conditions of the straight-line motion and single DOF. Finally, several potentially typical applications of the linkage are exhibited. The straight-line linkage has relatively simple joint layouts and kinematics model, and can be used as a deployable unit to construct some special deployable mechanisms.