Ultra-short radius sidetracking horizontal well has the advantages of short displacement before the target, small requirement on the size of sand body, high controlling degree over the drilled layer, and short drilling period. In order to solve the problems of high heterogeneity, uneven water injection efficiency and low recovery degree of low permeability sandstone reservoirs, a residual oil exploration test of ultra-short radius sidetracking horizontal well was carried out. According to the development situation of the research area and the requirements of sidetracking technology, standard of well and layer selection for ultra-short radius sidetracking horizontal well is established. Two methods of structure contour method and well inclination method are used to calculate formation dip angle in sidetracking direction. Based on data of sand body development characteristics, injection-production connectivity and water cut rising rules of the block, parameters of sidetracking horizontal wells for excavating different types of residual oil are designed and optimized. For low permeability reservoirs, separate sidetracking is not enough. Segmented fracturing is quite necessary to carry out for sidetracking horizontal well in order to maximize the exploitation function of the horizontal section. In the initial stage after sidetracking and fracturing, the average daily oil increase per well of the three test wells was 4.7 tons, and the average cumulative oil increase per well was predicted to be 1750 tons. Good oil increase effect and high economic benefits indicate that the new drilled horizontal branch from old vertical borebole can shorten the distance between injection and production wells, help establish effective displacement as well as greatly increase the seepage area, tap unutilized remaining oil, and eventually improve development effect of low permeability reservoirs.