The utility model relates to a micro-current sensor, which comprises an annular left support (1) and an annular right support (3), wherein one end of the right support (3) is connected with one end of the left support (1) through a latch (2), and the right support (3) can be opened and closed. A left upper cover plate (4) and a left lower cover plate (5) are respectively arranged on and under the left support (1), and a right upper cover plate (6) and a right lower cover plate (7) are respectively arranged on and under the right support (3). The left support (1), the right support (3), the left upper cover plate (4), the left lower cover plate (5), the right upper cover plate (6) and the right lower cover plate (7) form an annular placing groove, and a sensing module is arranged in the annular placing groove. The micro-current sensor has the advantages as follows: 1, the suitable frequency is 50kHz-30MHz, and the micro-current sensor can carry out accurate measurement to obtain a partial discharge signal; 2, errors can be reduced when different frequencies are measured; and 3, the sensitivity measurement achieves 5V/A, and a good effect is achieved in the sensor test.