The liftoff properties of the dimethyl ether (DME) jet diffusion flame were investigated experimentally and analytically with emphasis on the influences of flame stretch and fuel oxygen. The present experiments showed that the DME jet diffusion flame exhibited a distinct liftoff phenomenon that differed from other hydrocarbon fuels. This unique phenomenon was analyzed theoretically by taking into consideration the effects of flame stretch and the fuel oxygen. The results showed that the stretch effect had a significant impact on the critical liftoff Schmidt number and the flame liftoff height. Based on these observations, a new criterion for the lifted flame at the blowout limit was proposed. The results also demonstrated that the appearance of fuel oxygen in DME increases the fuel mixture fraction at the stoichiometric condition and changes the flame liftoff phenomenon. The effect of fuel oxygen was further investigated by adding air into propane and n-butane diffusion flames. It was found that with the increase of oxygen addition, both propane and n-butane flames change from the direct liftoff regime to the direct blowout regime. The results well described the unique liftoff phenomenon of DME and also applicable to other oxygenated and air diluted hydrocarbon fuels.