Hydrogen abstraction by NO2 from asymmetric methyl ethers by NO2 is theoretically investigated based on first-principles calculations in order to constrain their combustion models, including methyl ethyl ether(MEE), methyl n-propyl ether (MNPE), methyl i-propyl ether (MIPE), methyl n-butyl ether (MNBE), and methyl t-butyl ether (MTBE). We obtain the rate constants and branching ratios at 500-2000 K, and the dependence of reactivity on ether sizes and the reaction sites on the ethers. The cis-HONO channel is the most important one, followed by the HNO2 and trans-HONO channels. On the hand, the size of alkyl and the reaction site significantly affect the reactivity. Hydrogen abstraction mainly occurs at the C site (adjacent to the ether bond) of the long-chain alkyl. Moreover, the linear Bell-Evans-Polanyi correlation is observed for the hydrogen abstraction reactions between the asymmetric methyl ether and NO2.