When Global Navigation Satellite System(GNSS) receivers move in high dynamic environment, the Directions Of Arrival(DOAs) corresponding to interferences may change rapidly, which will reduce the performance of anti-jamming algorithm. A novel null widening algorithm based on signal power estimation is proposed. Firstly, according to the eigenvalues, the Sampling Covariance Matrix(SCM) is divided into signal subspace and noise subspace, and a set of linear equations is established based the signal subspace projection. Then, the signal powers around interferences are reset according to the required null width based on the linear equations. Finally, the Interference-plus-Noise Covariance(INC) matrix can be reconstructed with the reset signal power, based on which the weight vector is solved. Simulation shows that the proposed algorithm has a deeper null than other algorithms when the null width keeps the same, and the Signal to Interference Noise Ratio(SINR) of array output is also improved.