Abstract: With the help of 1-D radiation hydrodynamic code MULTI, we simulated the ablation process of a pulsed CO2 laser irradiation on a tin planar target. We studied the influence of pulse duration, peak power intensity and initial target density on electron temperature and density distribution at different time. Also, the optimum pulse duration for 13.5 nm extreme-ultraviolet (EUV) emission was obtained by statistical analysis. It is found that long pulse duration , for example, 100-200 ns, is better for EUV emission. In this paper, the mechanism is discussed combining electron temperature and density distribution. Laser energy is effectively absorbed in the critical density area, while absorption of laser energy and EUV in the underdense corona can be negligible. Using a long CO2 laser pulse to prolong the EUV emission time can improve conversion efficiency effectively. Meanwhile, the initial target density has little influence on tin plasma parameters.