Abstract: p-t of singlet oxygen generator (SOG) was experimentally proved to be a key parameter for the chemical efficiency of the chemical oxygen-iodine laser (COIL). In our small scale COIL device with square pipe-array jet-type SOG and chlorine flowrate of 94mmol/s, experiments revealed the strong dependences of O2(1D ) absolute yield on the p-t of SOG. Here, the O2(1D ) absolute yield is defined as the convertin g efficiency from chlorine. It was shown that the increasing of each unit of p-t led to nearly 10% absolute decreasing of O2(1D ) absolute yield. In our 5# COIL device with stable cavity, it was found the chemical efficiency increased significantly as the p-t decreased. So, for a given COIL device, it is essential to minimize the p-t of SOG as possible. The dependences of the p-t on some