The effect of NO addition on detonation initiation in the negative temperature coefficient (NTC) region for thermally stratified n-pentane/air mixtures is numerically modeled with detailed chemistry and transport. The emphasis of this paper is understanding how to control detonation initiation by altering its low-temperature reaction pathways with NO addition. It is found that in the NTC region, NO addition causes the temperature gradients of the 1st and 2nd ignition delay times to become countercurrent, which leads to detonation formation occurring in the negative normalized gradient area. This abnormal phenomenon is mainly attributed to the coupling between the countercurrent temperature gradients and the NTC effect. The current study advances the understanding of low-temperature chemistry in detonation formation and provides a novel concept to control detonation initiation in engines by adding chemically sensitive species.