The invention discloses a connecting rod gear type under-actuated pinching mechanism. The connecting rod gear type under-actuated pinching mechanism comprises gears, a linear motion mechanism, sectorgears, conveying rollers, spring devices, a universal coupler and a drive motor. The motion freedom degree in the horizontal direction is added to intermediate shaft gears and limited through springs,the opening and closing actions of roller gaps are controlled through the linear motion mechanism, the sector gears are driven by connecting rods to rotate around the axes of the sector gears, and the conveying rollers are driven to synchronously swing. At the moment when materials are clamped by working rollers, as the springs suffer from the effect of internal force of the connecting rods to besynchronously compressed in the horizontal direction, meanwhile, the gears move leftwards, when the roller gaps are opened, the connecting rod acting force borne by the springs disappears, and the springs restore to initial lengths. Instant clamping acting force is buffered through a spring system, the situation that clamped objects are damaged as clamping impact force is too high is avoided, clamped workpieces and parts of the clamping mechanism are protected to a certain degree, and the service life of equipment is effectively prolonged.