This study proposed a modified fluid flow algorithm merged with the particulate interface model in the particulate discrete element method to evaluate fluid transmission in rock fractures. The analytical solution of fluid transmission in a single fracture is first derived, then the theory of the modified fluid flow algorithm and the particulate interface model used in the particulate discrete element method are further introduced. To validate the correctness of the proposed model, the simulated hydraulic conductivity under fracture closure and dilation are compared with the analytical solution. After that, the simulated water head in a single fracture under un-shear and shear conditions are validated by the analytical solution. Furthermore, a re-meshing technique to handle the variation of pore mesh has been proposed to support the operation of the modified fluid flow algorithm during shearing. Finally, simple cases about fluid transmission in multiple fractures are demonstrated to prove the performance of the proposed model in investigating rock hydraulic problems.