In this paper, the moderate or intense low-oxygen dilution (MILD) technology was employed to reduce NOx emission index of the DME flame, whose NOx emission was expected high due to its higher adiabatic flame temperature. Experiments and modeling were conducted to study NOx emission mechanism of the DME-MILD jet diffusion flame. Various co-flow temperatures (T-co*) and oxygen concentrations (X-02*) were involved to investigate dependence of NOx emission mechanism on hot dilution level. NOx formation pathway in all subzones was clarified, employing the reaction path and sensitivity analyses. The results showed that for the DME-MILD jet flame, NOx was generated mainly through the NNH and N2O pathways, which was rather different from the traditional DME jet diffusion flame. EINOX increased gradually with the increment in X-02* or T-co*. A strong NO-NO2 conversion process and ultra-clean performance were verified for the DME-MILD jet flame. (C) 2016 Elsevier Ltd. All rights reserved.