Ignition delay times of dimethyl ether (DME)/propane/oxygen/argon mixtures at a pressure of 20 bar were measured in a shock tube at different DME blending ratios (0, 20, 50, 80, and 100%), equivalence ratios (0.5, 1.0 and 2.0), and temperatures (1100-1500 K). Validations of chemical kinetic models were made using available chemical kinetic models. A modified chemical model (Mod Mech C5) was proposed, and it can predict well the experimental ignition delay times and activation energies of pure propane, pure DME, and their blends. Both experimental and numerical results show that, with the decrease of the temperature, the logarithmic ignition delay time is increased linearly and activation energy is decreased slightly. With the increase of the equivalence ratio, the ignition delay time is increased for propane but decreased for DME. The ignition delay time is decreased with the increase of the DME blending ratio, and the reduction rate is increased with an increase in the equivalence ratio. Sensitivity analysis and radical pool analysis were performed to interpret the promoting effect of DME addition on the ignition of DME/propane mixtures.