Regarding the complex adjustment problem in the field-of-view(FOV) splitting, a FOV splitting scheme using dual rhombic prisms is proposed, and a high-accuracy optical extensometer is constructed. This scheme can not only simplify the adjustment steps of FOV splitting, but also increase the gauge length of extensometer by several times, and effectively reduce the effect of out-of-plane displacement on two-dimensional digital image correlation (2D-DIC) by adopting a telecentric lens. Uniaxial tensile test and continuous loading-unloading test were carried out to verify the feasibility and accuracy of the proposed method. The results show that the strain obtained by this method is in good agreement with those obtained by the strain gauge, and the root mean square error of the strain results is no more than 3 με. Therefore, the FOV splitting optical extensometer based on the dual rhombic prisms proposed in this paper is an easy-to-implement high-accuracy strain measurement technique.