This paper presents a planar Rogowski coil current transformer based on PCB for low current measurement. Its structure and working principle are given. Formula for calculating the coil's coefficient of mutual inductance is derived. Anti-interference mechanism of external magnetic field is analyzed. Experimental model is designed， and the test results show that the transformer model of rated 100 A has an accuracy of 0.2 for low current measurement， strong anti-electromagnetic interference ability and anti-DC interference ability. It is suitable for a special current converter of electronic power meter and relay protection， and can also be used for low current measurement in areas of anti-DC. So it has a positive significance for the development of new current transformer.