The invention relates to a method and a device for measuring a dip angle of a concentric coplanar trisected ring-circle nested polar plate and belongs to an angular surveying technique. The device is characterized in that an annular coplanar capacitance measuring head of a sensor unit consists of a round metal plate and three one-third circular-ring-shaped metal plates, wherein the four metal plates are coplanar and concentric with one another, the three one-third circular-ring-shaped metal plates are uniformly distributed along the circumferential direction, each one-third circular-ring-shaped metal plate can generate capacitance with the round metal plate, the annular coplanar capacitance measuring head is mounted on a round insulating substrate, the round insulating substrate is taken as a bottom surface of a cylindrical container, the cylindrical container is transversely arranged, insulating liquid equal to 1/2 volume of the container is injected into the container in a sealing manner, potentials of the four metal plates are extracted out by virtue of potential leads, the four metal plates are connected with an input end of a capacitance measuring unit through the four potential leads, and the capacitance measuring unit is connected with a dip angle calculating unit. According to the device and the method, when the container tilts, the relative positions of the annular coplanar capacitance measuring head and the insulating liquid are changed, and a dip angle value can be calculated by measuring the change of a capacitance value of a capacitor.