Low pressure premixed laminar dimethyl ether/oxygen/argon flames with different equivalence ratios (0.8, 1.0, and 1.5) were investigated experimentally and numerically. The major intermediates were identified, and their mole fractions were measured using molecular-beam mass spectrometry combined with synchrotron radiation photoionization. Simulations were performed using PREMIX CODE and a representative chemical reaction model for dimethyl ether. The influence of the equivalence ratio on the flame structure and reaction path of dimethyl ether was analysed. The results show that formaldehyde and methyl are the main Cl intermediates in dimethyl ether flames. Dimethyl ether is mainly consumed through H-abstraction reactions by H, OH, CH3, and O. The effect of these radicals on the H-abstraction reactions varies at different equivalence ratios. Most of the methoxy-methyl radicals formed by the H-abstraction reactions promptly undergo beta-scission into methyl and formaldehyde, with only a small amount reacting with oxygen under extremely lean conditions.