The ignition delay times (IDTs) of iso-octane with or without exhaust gas recirculation (EGR) in the 600-950 K temperature range and at pressures of 20 and 30 bar were measured under various equivalence ratios (Phi = 0.6-1.4) with the aid of a rapid compression machine. As for neat iso-octane IDTs measurements at 20 bar, it was found that the IDTs obtained in this work were consistent with the ones measured by other groups. Notable prolonging effects can be seen at the negative temperature coefficient region with EGR, which is independent of equivalence ratios. Moreover, the IDTs with EGR under fuel-rich and stoichiometric conditions showed a similar trend at both 20 and 30 bar. In the presence of NO in EGR, at a temperature of 632 K and temperatures above 732 K, the promoting effect of NO was observed, resulting in reductions of the IDTs. In parallel, the influence of NO was negligible in the 667-732 K temperature range. A comprehensive detailed kinetic model was employed to interpret the experimental data. The model performance was improved by adopting a high-level theoretical calculation of the 2HO(2) = H2O2 + O-2 reaction. Merging the N submechanism into the core model by considering the interactions between N-x and C-0-C-2 species can generally capture the influence of NO on the IDTs. Reaction path analysis indicated that the NO + HO2 = NO2 + OH reaction dominated in the presence of NO and its reaction rate increased as a function of temperature, which can explain the different IDTs behaviors with NO addition.