One-dimensional pre-mixed model for a pulsed chemical oxygen-iodine laser is presented according to the reaction mechanism in chemical oxygen-iodine laser. The influences of gas temperature of 150-450 K and pressure of 660-2660 Pa on single pulse energy, pulse duration and peak power are studied. The internal reason of the influences of pressure and temperature on laser characteristics is analyzed. The results show that the higher laser peak power can be obtained in the case of gas temperature of 150 K and pressure of 1330 Pa than in the case of 400 K and 2660 Pa. Thus an efficient pulsed chemical oxygen-iodine laser is promising if the abundant atomic iodine is generated instantaneously. The approach to atomic iodine generation does not disturb the state of supersonic flow.