Some questions exist in application of the relativity theory. To solve these questions, it comes up with the constant force balance axiom and derives the force transformation formula; comes up with the correlation analysis law to explain how to correctly apply the relativity theory; comes up with the absolute speed principle, correspondence principle and relative and absolute transformation principle to solve the real time and quality questions; comes up with universal gravitation double-balanced principle to solve the black hole existing question; and judges the impossible and practically significant time travel.