A drain current model of 2-D monolayer (ML) transition-metal dichalcogenide (TMD) tunnel FETs (TFETs) is proposed. For better accuracy, the proposed model features the following two points: 1) the accurate lateral energy profiles considering the extension of the depletion width (W-d) owing to the reduced dimensionality and 2) the spin- and valley-dependent complex band structure considering the spin- orbit coupling effect. The proposed model is validated by the tight-binding nonequilibrium green function simulation, in the case of ML MoS2 doublegate TFETs. By using the proposed model, the design guideline of ML TMD TFETs is presented.