The invention discloses a direction finding accuracy analysis method applicable to an arbitrary plane array. The direction finding accuracy analysis method includes the steps: building a coordinate system for the arbitrary plane array and positioning the geometric center of the array at a coordinate origin; evaluating direction finding accuracy of the array by a Cramer-Rao lower bound, and calculating important parameters including amplitude, direct-current offset and primary phase according to coordinates of antennas; listing function expressions about true azimuth angles and true pitch angles of the Cramer-Rao lower bound, and drawing a relation curve about the true azimuth angles and the true pitch angles of the Cramer-Rao lower bound according to the function expressions. If the Cramer-Rao lower bound within the range of a certain true azimuth angle and a certain true pitch angle is smaller, the direction finding accuracy of the position is higher. The direction finding accuracy analysis method is applicable to arbitrary application conditions in a transformer substation, and has a guiding function for optimizing layout of the antenna array. The antenna array optimized by the method has a high direction finding performance and a small array size.