We report on a first-principles study of a novel band modulation in zigzag double-walled boron nitride nanotubes (DBNNTs) by applying radial strain and coupled external electric field. We show that the band alignment between the inner and outer walls of the DBNNTs can be tuned from type I to type II with increasing radial strain, accompanied with a direct to indirect band gap transition and a substantial gap reduction. The band gap can be further significantly reduced by applying a transverse electric field. The coupling of electric field with the radial strain makes the field-induced gap reduction being anisotropic and more remarkable than that in undeformed DBNNTs. In particular, the gap variation induced by electric field perpendicular to the radial strain is the most remarkable among all the modu-lations. These tunable properties by electromechanical cou- pling in DBNNTs will greatly enrich their versatile applications in future nanoelectronics. We report on a first-principles study of a novel band modulation in zigzag double-walled boron nitride nanotubes (DBNNTs) by applying radial strain and coupled external electric field. We show that the band alignment between the inner and outer walls of the DBNNTs can be tuned from type I to type II with increasing radial strain, accompanied with a direct to indirect band gap transition and a substantial gap reduction. The coupling of electric field with the radial strain makes the field-induced gap reduction is anisotropic and more remarkable than that in undeformed DBNNTs. In particular, the gap variation induced by electric field perpendicular to the radial strain is the most remarkable among all the modu- lations. electromechanical couling in DBNNTs will greatly enrich their versatile applications in future nanoelectronics.