Abstract: The analytic formulary relations hips between current and voltage in inward-emitting coaxial diode are presented in this paper as well as the PIC numerical simulation and experim ental verification. Due to the 2-D effects, the analytic formulary can't exactly describe the characteristic of the current-voltage relationships in the diode. Hence, a numerical simulation code-KARAT is employed to study the 2-D effect s modification of this relation in different diode voltage level, and the modification coefficient vs. Different parameters are given. The intuitionistic pictures of the electron motion in the diode are also obtained. Meanwhile, the self-pinched current of inward-emitting coaxial diode is deduced. The experiment of coaxial diode was carried out on the SINUS-881 accelerator, and the