The invention discloses a method for measuring the current of a long straight conducting wire. A magnetic field around the long straight conducting wire to be measured is detected by using four or more single-axis magnetic sensors to obtain magnetic induction intensity; and based on the magnetic induction intensity, a first distance and a second distance are respectively calculated according to the magnetic induction intensity of the single-axis magnetic sensors and two groups of incompletely identical single-axis magnetic sensors. According to the method disclosed by the invention, based on the difference between the first distance and the second distance, the magnitude of the magnetic induction intensity of the position point of the single-axis magnetic sensor is adjusted until a magnetic induction value is more accurate, and the current of the long straight conducting wire is obtained accordingly. By adoption of the method provided by the invention, the interference of an external magnetic field on the magnitude of the measured current is eliminated from the algorithm, a more accurate current value of the long straight conducting wire can be obtained, and no magnetic core needsto be used, so that the operation is simple. The invention further provides a device and system for measuring the long straight conducting wire current, which have the above beneficial effects.