A power frequency zero-flux mini-current sensor for capacitive equipment dielectric loss on-line monitoring comprises a working magnetic core 1, wherein a test coil 3 is winded round the working magnetic core 1, a secondary side coil 2 is winded round the test coil 3 in the inverse direction, shielding layers 4 are arranged between the secondary side coil 2 and the test coil 3, and the test coil 3 and the working magnetic core 1, the test coil 3 is connected with a compensation circuit module 5, the output end of the compensation circuit module 5 is connected with one end of the secondary side coil 2, the other end of the secondary side coil 2 is connected with an output circuit module 6, the two ends of the test coil 3 generate induced potential, the induced current is added to the output end of the compensation circuit module 5 to generate secondary current for the secondary side coil 2, the compensation circuit module 5 is used to test the potential difference of the test coil 3, the magnetic flux in the working magnetic core is almost equal to zero; and if the test value deviates the permissible value, the working magnetic core can be adjusted automatically to keep in almost zero-flux state, and the mini-current sensor has high reliability and is characterized by simple structure, little production difficulty and low cost.