The inversion and gain of the electron-collisional excitation pumping X-ray laser depend on four parameters (electron density Ne, electron temperature Te, width of gain region D R and velocity gradient of lasing medium dv/dz) describing the internal state of plasmas. As an example, the dependence of the inversion and gain of laser lines at 19.6nm, 23.2nm and 23.6nm in neon-like germanium ion on Ne and Te is studied in this paper. In the gain region with a typical spatial width (D R=100m m）and velocity gradient of lasing medium (dv/dz=1.3 109s-1）,the effect of resonance lines-trapping on the gain is discussed and the objective regions of gain are given for these laser lines. In addition, the effect of dielectronic recombination process on charge-state distribution is discussed.