This paper presents a new method for current or voltage phasor calculation（PC）. The method uses the cosine filter（CF） and amplitude-frequency coefficient correction to filter out the real part of a phasor at the present sampling， and the imaginary part of the phasor at the a-quarter-period-before sampling. With this method， it is possible to calculate the phasors adaptively without any hardware changing sampling interval. It has characteristics such as amplitude-frequency consistency， phasor-frequency orthogonality， fine dynamic convergence， less calculation burden， and has no need to add differential filter to remove direct current（DC） component.