A humanoid robot arm with both shoulder joint and elbow joint is built. It is actuated by pieces of Mckibben muscles. Its skeleton-muscle formation is similar to the anatomical structure of the human arm. A pneumatic experiment system is established for supporting and testing the robot arm. The relationship between the robot arm actions and the Mckibben muscles is studied. Some main actions of the robot arm including the elbow bending, the whole arm arising and the rotating around the arm axis are realized.