The invention relates to a unilateral current based half-wavelength circuit free wave energy protection phase selection method. The protection phase selection method comprises the steps of filtering fundamental components from current based on phases; performing integration on the sampling value of the current variable quantity after the fundamental components are filtered, wherein the integration interval is matched with the integration intervals in the free wave energy protection sections I, II and III; distinguishing internal and external faults by comparing the magnitudes of the free wave energy after fault comparison; enabling phase selection elements and free wave energy protection to be matched, and then outputting through an AND logic outlet to realize fault phase selective tripping. By adoption of the technical scheme, the problem that fault phase selection cannot be carried out through the free wave energy protection due to the reason that the quadratic sum of the three-phase current is required in the protection criterion of the free wave energy protection is solved.