Effects of diluent gases composition on ignition delays of dimethyl ether (DME) were investigated at compressed pressure of 1.5MPa, compressed temperature from 670K to 795K and equivalence ratio of 1 by using a rapid compression machine (RCM). The diluent gases considered were nitrogen (N2), mixture of N2 and argon (Ar) at mole ratio of 50% to 50% and mixture of Ar and carbon dioxide (CO2) at mole ratio of 61.2% to 38.8%. The simulation study was performed over a wider temperature range based on CHMKIN-PRO software. The results showed that diluent gases composition had little impact on the first-stage ignition delay. However, significant differences in the total ignition delay were observed, especially in the negative temperature coefficient (NTC) region. Compared with N2, mixture of N2 and Ar decreased the total ignition delay by 30%. The chemical effect of diluent gases composition on the first-stage and total ignition delays was negligible. The thermal effect was dominant factor in the low temperature and NTC regions, however, the chemical effect of CO2 enhanced and exceeded the thermal effect in the temperature region beyond the NTC region. With the increase of N2 dilution ratio, the first-stage ignition delay was slightly increased, while a significant increase in the total ignition delay was observed. Moreover, the NTC behavior of total ignition delay was noted to become more pronounced at high N2 dilution ratio.