Hydraulic fixture can ensure the accurate positioning and firm clamping of the workpiece at the specified position, reduce the vibration and deformation during machining through floating support, and make way for the clamping position during machining by automatically controlling the pressing and lifting of the platen. Hydraulic fixture can not only bear large cutting force in rough machining, but also ensure accurate positioning in precision machining, and can also complete the support, clamping and quick unloading that manual fixture can not complete.