The invention provides an adjusting mechanism. The adjusting mechanism sequentially comprises a foundation, an X-direction structure, a theta-direction structure, and a Y-direction structure from bottom to top; the X-direction structure comprises an X-direction positioning and adjusting module, an X-direction adjusting component, and an X-direction sliding plate; the theta-direction structure comprises a theta-direction positioning adjusting module, a theta-direction adjusting component, and a positioning rod; and the Y-direction structure comprises a Y-direction positioning adjusting module,a Y-direction adjusting component and a Y-direction sliding plate. In the adjusting mechanism, all axes are driven to move based on the rotation of the adjusting components. The structures of the three directions are organically combined and are not interfered with one another. The mechanism is easy to manufacture and is simple and reliable in assembly and the manufacturing cost is low. The horizontality of the adjusting mechanism can be adjusted, the X-direction, Y-direction and theta-direction position adjustment on the horizontal plane can be realized, and the mechanism is easy to operate.The requirements on the horizontality, positioning accuracy and the like of an installation plane can be reduced, and the six-freedom-degree position adjustment can be performed according to actual requirements in the process of integration and debugging of a system.