an equivalent operator of radial operator is resulted. Though the radial operator itself is non-self-adjoint and is not

measurable in physics，the equivalent operator is in fact the difference of two self-adjoint operators，so is measurable.

Thus，a superficial contradiction between the non-self-adjointness and existence of the uncertainty for the radial

momentum operator is resolved. What is more，the Hydrogen atom ground state is used to show how to measure

the equivalent operator.