The principle of relativity requires that the expressions for particle’s momentum and energy take the same functions of the particle’s velocity in all inertial frames.The mass-velocity relation of relativity is derived independent of conservation laws. It direct proves that neither conservation laws nor the Lorentz transformation is a necessary condition for mass-velocity relation.From the mass-velocity relation，the generalized Lorentz transformation formula of inertial frames can be obtained. The proof implies that the mass-energy equivalence and the massvelocity relation of relativity are more fundamental than the Lorentz transformation formula in relativity.