Circular sample window method is not applicable for joint surveying in field. A uniform data structure is designed for joint data of all trace types. The joint trace map is drawn according to field surveying data，and circular sample windows are arranged on the joint trace map. The position，quantity and radius of the circular windows are adjusted to the specific conditions of surveying data. Simultaneously，the quantity of different trace types in the same circle is identified and recorded. Based on the circular sample window method theory，the trace midpoint density of joint is obtained to estimate the mean trace length. The distribution of the trace midpoint is not uniform，and it is far from being insignificant for reasonable results that position and radius of circular sample window are selected appropriately. Concentric circle method and tangent circle method are applied to estimating the mean trace length and the trace midpoint density in Jiji quarry. It indicates that tangent circle method is stable and reasonable. The joint data，which are surveyed in the candidate region of high radioactive waste in Beishan Mount，Gansu Province，China，are analyzed with tangent circle method. As a result，the influence range of the fault is concluded by analyzing the mean trace length and the trace midpoint density of joint on the both sides of the fault.