The estimation of synchrophasor is of great concern for power quality and protection in power system. Once the power frequency deviation is present, the phasor would undergo a rotation in the complex plane. This phenomenon will introduce difficulty for the interconnection of power grids and distributed generation systems. In this paper, a synchrophasor estimator with the two-stage ADALINE is introduced to deal with the estimation errors due to power frequency deviation. With the compliance tests in IEEE Std. C37.118-2005, the performance of proposed solution structure can be verified.