Abstract: According to the calculating result on Ne-like Ar X-ray laser pumped by capillary discharge, with code XDCH(1D radiation magneto-hydrodynamics coupled to time-dependent rate equations), this paper presents the whole process of producing gain of 46.9nm laser line. It is shown that higher gain came from higher population of Ne-like ion and faster change of electron temperature and density, different from the lower gain in situation of static state. With the analysis on the viewpoint of atomic kinetics, some helpful advice to experiments are put foward.