The seepage-stress coupling characteristic of practical engineering rock mass under 3D unequal principal stress is a key point in the academic and engineering fields. A reasonable formula for stress-seepage coupling characteristics of rock mass with a single rough joint is deduced based on the theoretical analysis. The feasibility of the theoretical expression is verified by the indoor true tri-axial stress-seepage coupling tests. Based on the test data， a reliable empirical formula is given by the powerful data fitting software. The numerical experiment is carried out by the 3D distinct element method. The difference of the methods on choosing joint normal stiffness parameter is discussed. The empirical formula is also verified by the numerical simulation based on reasonable assigned parameter values. The theoretical analysis is fully tested by the indoor true tri-axial stress-seepage coupling tests， the credible non-linear fitting and the numerical simulation.