The utility model relates to a chuck. The chuck comprises a main frame, a main shaft and a clamping mechanism. An axial through hole is formed in the main shaft so that a to-be-clamped piece can penetrate through the axial through hole. Wherein the main shaft is installed in the main frame, the clamping mechanism comprises a chassis and clamping assemblies, the chassis is arranged on the main shaft in a sleeving mode, the multiple clamping assemblies are arranged at intervals, each clamping assembly comprises a clamping jaw, a sliding block and a pressing plate, the clamping jaws are installedon the sliding blocks, sliding grooves are formed in the chassis, the sliding blocks are slidably arranged in the sliding grooves, and the pressing plates are installed on the chassis and abut against the sliding blocks. Chuck, the sliding block is slidably arranged on the chassis; pressing plate fixing, the pressing plate can adjust the gap between the sliding block and the sliding groove through match grinding. The self-centering precision of the chuck is prevented from being influenced by looseness of the sliding block due to an overlarge fit clearance, the faults of loose clamping or difficult loosening of the clamping jaws due to unsmooth operation of the sliding block due to an oversmall clearance are avoided, the clamping precision of the chuck is improved, meanwhile, long-time movement abrasion of the sliding block in the chassis can be solved by replacing the pressing plate, maintenance is convenient, and cost is low.