Ignition delay of syngas is an important factor that affects stable operation of combustor and adding diluents to syngas can reduce NOx emission. This paper used H2O, CO2 and N-2 as diluents and calculated ignition delay of syngas in temperature range of 900-1400 K and at pressures of 10 and 30 atmrespectively. In high temperature range, comparing with N-2 dilution, adding H2O and CO2 can significantly inhibit autoignition of syngas because they have higher collision efficiencies in reaction H + O-2 (+M) = HO2 (+M). As for low temperature conditions, adding H2O can increase reactivity of syngas, especially under high pressure, because of its high collision efficiency in reaction H2O2 (+M)= 2OH (+M). Comparing with different dilution rates shows that for syngas and operating conditions in this paper, adding N-2 mainly influences temperature rising process of syngas combustion, thus inhibiting reactivity of syngas. In addition, this paper calculated ignition delay of syngas at different equivalence ratios (phi= 0.5, 1.0). Higher equivalence ratio (phi <= 1) means that less air (especially N-2) needs to be heated, thus promoting ignition of syngas. (C) 2016 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.