The electronic structure of van der Waals (vdW) TaS2/TaSe2 and TaSe2/TaTe2 heterostructures has been investigated by first-principle calculations at different electric fields. All the monolayer 1T-TaX2, TaS2/TaSe2 and TaSe2/TaTe2 heterostructures are metallic, where Fermi level goes across the conductance band at a zero electric field. Spin splitting appears in TaS2/TaSe2 heterostructure at an electric field from -0.1 to -0.5 V/angstrom, and gradually decreases with the increase of electric field. Whereas the spin splitting slowly increases when the electric field increases from 0.1 to 0.3 V/angstrom. Furthermore, the band structure of TaSe2/TaTe2 heterostructure is similar to TaSe2/TaTe2 one. However, at an electric field of 0.3 V/angstrom, the TaSe2/TaTe2 vdW heterostructure is an indirect-band -gap semiconductor with a gap of 0.690 eV, suggesting that the electric field has a great effect on the band structures. Our results can bring more significant basis for nanoelectronic device.