The band structure model of commensurate double-walled carbon nanotube (DWNT) was built by using tight-binding Hamiltonian with curvature effect included. The field emission characteristics of commensurate DWNT were quantitatively investigated basing on its dependence on the band structure. The results indicate that interwall coupling interaction (ICI) can form additional electronic energy level in the band structure of DWNT so as to increase the emitting channel of electrons;and at the same time, it can also increase the energy gap of the metallic DWNT and decrease that of the semiconducting DWNT, which will result in a change in the number of electrons emitted from the valence band. At a given applied electric field, the emission current of DWNT has an obvious increase, compared with that of DWNT when ICI is turn off, and the current increment of semiconducting DWNT is larger than that of the metallic one. At an applied electric field of 5V/μm, the field emission currents of commensurate DWNTs (6,6)&(12,12), (10,0)&(20,0) and (8,2)&(16,4) have an increase of about 3%,10% and 4%, respectively, compared with those when ICI is turn off. The results reveal that ICI contributes to the transport and electron emission of DWNT, which is helpful for understanding the field emission mechanism of DWNT ,and hence that of MWNT.