Abstract: Through analyzing anatomical structure of human hand and observing human hand motion,two viewpoints are proposed:(1)the metacarpal-phalangeal joint(MPJ)of human index finger has two rotational degrees of freedom(DOFs)with perpendicularly intersecting axes,and the kinematic models derived from different arrangement sequences of the intersecting axes are different,one of which is more approximate to human finger's MPJ;(2)the two rotational DOFs of MPJ are coupled at their extreme positions.The workspace of index finger is depicted through experiment.Then it is compared with that of two possible kinematic models,and the actual kinematic structure of MPJ is determined.In addition,the coupling motion of this joint is validated.Finally,kinematic model of finger is presented based on the aforementioned investigation,which conforms to the actual structure of human hand.