The time behavior and the optimum conditions for the Xe gas capillary discharge extrem ultraviolet source are investigated theoretically and experimentally. By setting up a one-dimensional magneto-fluid-mechanics model, the plasma compressing characteristics and the emission characteristics are simulated under different gas pressures and different discharge currents. The time characteristic and the intensity of the 13.5 nm (2% bandwidth) emission are measured experimentally. The theoretical and experimental results show that there are the optimum gas pressures for different discharge currents. Meanwhile, the optimum gas pressure increases with the discharge current increasing. Moreover, the time to generate the highest 13.5 nm (2% bandwidth) emission should decrease by the increase of the discharge current. All the results should be useful to better understand the plasma condition for the discharge experiments and the EUV source. And it can be used to increase the power of the extreme ultraviolet source as well.