The work aims to propose a labeling mechanism based on closed-loop parallel mechanism to carry out the kinematic analysis, study its degree of freedom and workspace and verify its effectiveness, so as to improve the universality of labeling mechanism and solve the labeling problems on surfaces with different inclinations in assembly line. The model of parallel mechanism was established, the freedom degree of the mechanism was analyzed by the screw theory, and then the inverse kinematics solution of the mechanism was obtained by the closed-loop vector method. The calculation function of Matlab and the three-dimensional coordinate search method were used to solve and draw the workspace of the mechanism and analyze the maximum rotation degree of the mechanism at different points. The parallel mechanism had 2 kinds of movements and 1 rotational freedom. The workspace was compact, void-free and regular in shape. The maximum rotation angle of most workspace in vertical direction could reach 90°. The parallel mechanism has simple structure, large rotation angle in vertical direction and easily adjusted rotating center of the moving platform. Combined with the inherent advantages of parallel mechanism, such as high stiffness, stable structure and small inertia, the labeling task of irregular products on the assembly line can be completed efficiently.