The invention discloses a grounding grid branch circuit resistance detection method based on a ++-shaped detection unit. The grounding grid branch circuit resistance detection method comprises the following steps: according to the connection situation of a grounding grid branch circuit to be detected and ambient branch circuits, establishing a++-shaped detection unit; selecting no less than seven pairs of upstream grounding bodies, sequentially injecting current from one point and drawing out current from anointer point, and measuring the voltage of the upstream grounding bodies in the++-shaped detection unit and the current of the grounding grid branch circuit to be detected at the moment; establishing four equations according to the measured voltage and current data, and solving each equation step by step, thereby finally obtaining the resistance of the grounding grid branch circuit to be detected. The whole detection process is simple and small in calculation amount.