The invention relates to a crank block type under-actuated robot finger device belonging to the technical field of humanoid robot fingers and comprising a first finger part, a second finger part and an under-actuated joint. The under-actuated joint comprises a driving block, a joint shaft, a spring, a first shaft, a connecting rod, a second shaft and a drive plate; the spring is connected with the first finger part and the driving block; the connecting rod is respectively articulated with the driving block and the drive plate which is fixedly sleeved on the joint shaft; and the driving block is embedded in the first finger part. The device adopts the crank block mechanism to realize the rotation function of the second finger part, and the very short movement distance of the driving block can bring the large-angle rotation of the second finger part through reasonable dimension design; the device can coordinate with other driving fingers or driving joints to capture an object, has self adaptability, few driving parts, a short driving chain and low cost and is similar to human fingers, can be connected in series to form highly under-actuated multi-joint fingers and is applied to humanoid robot fingers.