Reinforced blocks are common anchorage forms for external tendons. However, there was no mature design method. Through finite element analysis, the paper revealed that the tensile stress concentration was caused by three typical local actions. On this basis, three equations for calculating resultant forces of these local actions were formulated. Thus a quantitative reinforcement design method of anchor blocks was proposed. Finally, an anchor block of the Fourth Nanjing Yangtze River Bridge was presented as a design example to demonstrate the effectiveness and convenience of the proposed method.