The invention relates to a tool clamp in machining, and in particular to a simple screw clamping mechanism. The simple screw clamping mechanism comprises a base. A vertical hollow part is formed on the base, and a clamping block is arranged in the hollow part. The upper end of the clamping block is fixed to the hollow part of the base through a locating pin. The lower end of the clamping block is connected with one side of the base through a spring, and a handle is arranged at the position, opposite to the spring, of the other side of the base. The handle rotates inwards to compress the clamping block, the clamping block is driven to clamp a workpiece, and the clamping function is achieved. Conversely, the handle rotates outwards, elastic force is generated on the clamping block by the spring at this moment, the clamping block is driven to loosen the workpiece, and the workpiece is rapidly mounted and demounted. Furthermore, due to the fact that the locating pin is arranged at the end close to the workpiece, torque analysis shows that the workpiece can be clamped only through small force of the handle on the clamping block, and therefore the labor saving effect can be achieved.