The invention discloses a microwave sensor for measuring a dielectric constant and magnetic conductivity of a magnetic medium material. The microwave sensor comprises a microstrip line structure, a medium layer, a metal sheet and a slotted metal CSRR (complementary split-ring resonator) structure from a top layer to a bottom layer. The slotted metal CSRR structure is composed of an inner slot ringand an outer slot ring, wherein each of the inner slot ring and the outer slot ring is provided with an opening, and facing directions of the openings are identical; two opposite right angles of theopening of the inner slot ring and two opposite right angles of the opening of the outer slot ring are all folded inwards in an alignment mode, and the opening of the outer slot ring extends towards the inside and outside of the outer slot ring to form channels; the part between the channels of the opening of the outer slot ring is a region with maximum magnetic field intensity, and the region isused to contain a to-be-detected sample for measuring the magnetic conductivity of the sample; and the part between the channels, where the two inwards-folded right angles of the inner slot ring and the two inwards-folded right angles of the outer slot ring are connected, is a region with maximum electric field intensity, and the region is used to contain the to-be-detected sample for measuring the dielectric constant of the sample. According to the microwave sensor, the dielectric constant and the magnetic conductivity can be measured simultaneously in different regions of the same sensor, the sensor has extremely high sensitivity and Q value, and the accuracy of measurement is guaranteed.