The invention discloses an optimal arrangement method of an UHF phased array used for substation partial discharge direction finding. The optimal arrangement method comprises the steps of: 1) making a number of array elements and array element spacing of the phased array unchanged, deriving Cramer-Rao low bound expressions in different geometric shapes, and optimizing a geometric shape of the UHF phased array; 2) making array element spacing of the phased array after geometric shape optimization unchanged, drawing a relation curve between direction finding errors and the number of array elements in numerical simulation, and optimizing the number of array elements of the UHF phased array by combining with a construction cost of an acquisition system; 3) and acquiring partial discharge signals in a substation for the phased array after geometric shape and array element number optimization, analyzing frequency spectra of the signals, and optimizing array element spacing of the UHF phased array. The optimal arrangement method adopts the UHF phased array which is small in size, has the advantages of high anti-interference ability and high spatial resolution, and is convenient for partial discharge patrol inspection.