Owing to the inability of the power measured with conventional instruments not to correctly reflect the actual power state at the electric energy measuring points， the four-quadrant power measuring principles and implementation for measuring and analyzing the power of electric power signals are proposed. First an in-depth analysis is made of the principles of four-quadrant power measurement， by which the power is analyzed from the point of view of the vector to uniquely determine the true state of electric energy exchange， thus increasing the accuracy and applicability of power measurement. As an effective method for measuring and analyzing the electric power signals， it is applicable not only to power measurement at electric energy measuring points with definite power transmission direction but also to that with variable power transmission direction. Then two implementing methods are given， the indirect method and direct method. Finally， the results of simulation are given， which show that the above-mentioned principles and implementing method are correct and feasible.