相对性原理要求粒子的动量和能量对于速度的依赖关系在不同的惯性系中具有相同的函数形式，由此无需利用守恒定律和洛伦兹变换公式直接推导出相对论质速关系，证明了守恒定律和洛伦兹变换公式都不是推导相对论质速关系的必要条件.由相对论质速关系进一步可得到惯性系的广义洛伦兹变换公式，从而揭示了质能关系和质速关系是比洛伦兹变换公式适用范围更广的相对论基本公式.

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.