According to the characteristics of a novel continuous UHPC box-girder bridge and the layout of its prestressing system, the anchor block for external tendons on the web was studied. Firstly, the effect of the plate thickness on the “local bending effect” in anchorage zone was evaluated through the analysis of stress in the isolated rectangular anchor block. A simplified plane linkage model was proposed through the topology optimization in order to study the force transfer mechanism in anchorage zone. Moreover, two kinds of methods were developed to strengthen the anchorage zone based on the simplified model. On the basis of the above research procedure, six different anchoring schemes of the anchor block for the external tendons were designed. After analyzing and comparing the performance of the different anchoring schemes, the effects of diaphragms, steering of prestressing tendons, and anchoring length of the anchor block on the mechanical behavior of the anchorage zone were evaluated. Finally, a type of reasonable anchor block of the external tendons was obtained.