A new approach is presented to produce core plasma poloidal rotation during electron cyclotron resonance heating (ECRH) in Tokamaks. The physical mechanism employed here is as follows:in a Tokamak plasma with high power ECRH, the resonance particle localization causes poloidal electric field, which consequently induce a poloidally asymmetric ion profile. This kind of poloidal ion accumulation would overwhelm the damping of poloidal rotation from the magnetic pumping, and make the plasma spin up poloidally. Based on the fluid equations and the drift kinetic equation, we have derived the criterion of plasma spin up in the collisionless region. It is shown that the core plasma poloidal rotation can be generated by ECRH in the practical rf power level.