An experimental investigation was performed on the effects of temperature, pressure, equivalence ratio and fuel concentration on ignition delay times of DME/O2/Ar mixtures behind the reflected shock wave. Experimental conditions are over temperatures of 1000 - 1600 K, pressures of 1.2 - 20 atm, equivalence ratios of 0.5 - 2.0 with fuel concentrations of 0.5-2.457%. The measurements showed that the DME mixtures have different global activation energies under different equivalence ratios and thus correlations were derived under different equivalence ratio based on all experimental data, which fits fairly well with the experimental data. Four recently developed models were compared to the measurements and the results showed that LLNL DME Mech under-predicts the ignition delay times of DME at p = 1.2 atm, indicating further improvement is required. Finally, a systematic kinetic chemical analysis was performed to chemically interpret the observed equivalence ratio dependence and to ascertain the key reactions that control ignition of DME, which are the potential candidates for improvement of LLNL DME Mech.