Degrees of freedom (DOFs) and workspace are important factors to evaluate the flexibility of the dexterous hand. This paper develops an original dexterous hand, which has 20 active DOFs and adjustable thumb. Imitating the human hand bone structure, we design a full driven multi-fingered anthropomorphic robot hand (YWZ dexterous hand). For the thumb of YWZ dexterous hand, we innovatively design a metacarpal phalange mechanical structure to adjust thumb’s assembly position and radial orientation relative the palm. We construct coordinate systems to deduce the finger kinematic equations and analyze the finger workspace. A physical prototype of YWZ dexterous hand was manufactured to test its kinematic characteristics and workspace. Experimental results validate the YWZ dexterous hand has large workspace, excellent operating flexibility.