At present, the planning and controlling problems of grasping in robotic multi-fingered hand system have not been solved perfectly for the objects with different sizes and shapes. Therefore, it is proposed to improve the dexterity of the robotic multi-fingered hand and expand its working space by using humanoid palm to reduce the difficulty of grasping planning and controlling. Firstly, the characteristics of human palm movement were analyzed and a robotic alterable palm mechanism of a humanoid hand was developed based on the skeletal structure of the human palm. The alterable palm mechanism had six degrees of freedom, and the fingers on the alterable palm mechanism were able to change the working space and the grabbing point position by the configuration transformation. Then, the mathematical model of the alterable palm mechanism was established, and its six degrees of freedom were analyzed when the number and position of grasping point were known. Then, the model of alterable palm mechanism was established by three-dimensional software to simulate the grabbing action. Lastly, the grasping experiment was carried out through the experimental platform and the physical prototypes to verify the grasping ability and adaptability of the alterable palm mechanism by grasping 13 kinds of objects with rigid and flexible fingers. It could be seen that the robotic alterable palm mechanism of a humanoid hand was able to realize the adaptive configuration simply and quickly, and it could complete the grasping of objects with large differences in size， weight and shape. It was suitable for grasping by two, three or four fingers and able to be connected with rigid or flexible fingers, which not only improved the grasping quality and adaptability of the robotic multi-fingered hand, but also reduced the difficulty of grasping planning and controlling. The research results provide reference for the universal application of robotic multi-finger hand.