The invention discloses a positive-sequence current cross brake method for preventing transformer homodyne protection misoperation. Through taking a maximum zero-sequence current and a maximum negative-sequence current of each side of homodyne, the ratio of the maximum zero-sequence current to a maximum positive-sequence current is calculated, and when the ratio of the maximum zero-sequence current to the maximum positive-sequence current is greater than a threshold fixed value, it is considered that a fault is generated and homodyne protection is started; and if the ratio is smaller than the threshold fixed value, it is considered that a non-grounding fault occurs, and the homodyne protection is locked. According to the invention, cross braking is carried out on a positive-sequence current by use of the maximum zero-sequence current and the maximum negative-sequence current of each side of the homodyne, phase fault homodyne misoperation outside a region is prevented, absence of a three-phase CT at a neutral point of a certain-side CT of the homodyne and operation rejection of the homodyne protection when the power supply end at the winding side of a transformer is not grounded are also effectively avoided, the homodyne protection reliability is improved, the simplicity and the practicality are high, a positive-sequence current brake coefficient of each side of the homodyne does not have to be calculated, what is needed is only to calculate the positive-sequence current brake coefficient once, the computational complexity is reduced, and realization of microcomputer protection is facilitated.