Nowadays the most popular tolerance analysis method in use is to obtain the tolerance design function through the assembly dimension chain, however not suitable to manufacturing of the robots with complex structure and high precision. With only considering the case based on the error of the active joints, through the establishment of mathematical model of error, orientation error and position error were analyzed, and a detailed analysis result of the structure of parallel robot with three degrees of freedom (3DOF) was obtained. Based on numerical analysis method, an effective method is provided for calculation of the orientation error and position error of robot under a given standard configuration.