The invention provides a current sensor based on a magnetic concentrating and magnetic shielding double function magnetic conductive loop and magnetic fluid. The current sensor comprises a magnetic conductive loop, shielding covers, a sensing head, an optical fiber coupler, a spectrograph and a broadband optical source. The magnetic conductive loop is a rectangular loop with one side provided with a slit. Magnetic conductors arranged at the two sides of the slit are respectively wrapped by one rectangular magnetic shielding cover. The sensing head is arranged in the magnetic concentrating area or the magnetic shielding area in the slit. The sensing head is radially parallel to two conical top end planes. Broadband light emitted by the broadband optical source enters the sensing head through the optical fiber coupler. Light signals reflected by the sensing head enter the spectrograph through the optical fiber coupler. According to the technology, the problem of birefringence of the current sensor based on the Faraday effect and the problem of the hysteresis loop of the current sensor based on giant magnetostrictive material can be avoided, and a magnetic field generated by a tested lead is enabled to form the magnetic concentrating area and the magnetic shielding area in the magnetic loop slit through the double conical magnetic conductive loop with the shielding covers.