The measurement of velocity field and shear strain rate using PIV has been performed in order to clarify the mechanism of NOx reduction in the opposed impinging jet combustor. It was found that the highly strained fields are distributed in broad regions of the main combustor using smaller orifice diameter of the prechambers. The strain rates are known to play an important role in increasing ignition delay time in the main combustor. During the ignition delay time, the flow characteristics of the main combustor are changed to the highly turbulent flows and then reignition can occur so that the main combustion time can be decreased significantly by a factor of 2. Hence, the emission of NOx can be reduced keeping the combustor pressure at the high level. This is believed to be the fact that the fully turbulent flows enhance the intermolecular mixing between cold and hot spots. As a result, the hot spot temperatures are decreased and thus the low emission of NOx is produced in the impinging jet flame combustor. It is also noted from Borghi Diagram that the combustion phase moves from the flamelet regime to the distributed reaction regime.