The invention relates to a machining positioning device, in particular to a machine head structure with an eccentric clamp. The machine head structure comprises a machine head box, a main shaft and the eccentric clamp. The main shaft is arranged in the machine head box, one end of the main shaft stretches out of the machine head box and is connected with the eccentric clamp, and the eccentric clamp is provided with a clamping oil cylinder, a crank and a V-shaped table. When a mechanism works, a workpiece is placed on the V-shaped table, the crank is driven by the clamping oil cylinder to swing, and the crank is provided with a pressing head used for fixing the workpiece. The machine head structure is high in rigidity, precision and efficiency, and multiple eccentric crankshafts can be machined by adjusting local components.