It is well-known that Vth-Pelgrom plot of haloimplanted transistors show non-monotonous behavior in long channel region where analog circuits are usually designed. However, none of the preceding works have presented physically based predictable model for this phenomenon. In this paper, a compact model which can predict the non-monotonous behavior of the Vth-Pelgrom plot of long channel halo-implanted transistors with respect to the change of their impurity profiles and/or device structures has been presented for the first time. The model is derived by combining the expressions of Hueting’s GCH model and Pang’s analytical surface potential model together with proper approximation. The model can accurately reproduce measurement results and also can predict how Vth variation changes with respect to halo and channel profile variation. It is also shown that there is a high sensitivity band of Vth variation in halo versus channel doping level space.