Chemical Reactor Network approach has great advantages in emission prediction research and one-dimensional design of combustors. It can use detailed chemical reaction mechanism and substantially shorten the computing time. This paper uses it to calculate the optimum air distribution scheme of a low NOx annular combustor. The combustor is divided into several zones based on the flow filed characteristics. First, the total air amount is divided into two parts, the first half air flow of annular combustor including swirler and primary holes, and the last half air flow including cooling holes and dilution holes. Air flow of these two parts is confirmed. After analyzing all reactor data and comprehensively considering all aspects of the factors, air flow mass fraction of each zone is confirmed for the optimum air distribution scheme. The effective volume of each zone and the one-dimensional combustor lengths are calculated using Differential Element method. The NOx and CO emission under the optimum air distribution scheme and exact effective volumes are proved much lower than general level.