An analytical potential model for threshold voltage of asymmetric Double Gate MOSFET (DG MOSFET) is derived by considering mobile charges. A cubiod function approximation is made for potential distribution of analytical solution of 2-D Poisson's equation. Different gate work functions are considered for both tied and independent DG MOSFET.The threshold voltage behavior of DG MOSFET for different body and oxide thicknesses is investigated. The analytical solution of threshold voltage is verified through TCAD simulation and is compared with existing threshold voltage model reported without consideration of mobile charges. The model developed considering the mobile charges, agree satisfactorily with other theoretical predictions.