This paper proposed a zero-sum magnetic field integral technology to minimize the crosstalk effect in straight light path optical current transducer. The discrete Ampere’s law was proposed and studied based on analyzing of the magnetic field integral along a discrete loop, and its mathematical model was established. The S^m model of regular polygonal discrete loop and the mS^m model of S^m regular distribution were discussed. The results showed that the S^m model possessed 2m zero-sum points, and the currents which placed on the zero-sum points did not contribute to the magnetic field integral result of S^m model. The origin point interchanged with the zero-sum point when any two S^m models of the mS^m model switched places. Based on that conclusion, the zero-sum theorem of S^m model and the reciprocal theorem of mS^m model were proposed. The discrete Ampere’s law, the zero-sum theorem of S^m model and the reciprocal theorem of mS^m model together made up the theory system of magnetic field integral along regular polygonal discrete loop, which still met the Ampere’s law.