BSD Wellbore Repairing Agent for Drilling Fluid is composed by Nano polymer particles, Modification of natural fibers, Elastic particles and Granular material. Variability as the Nano polymer particles have and Network structure as the Modification of natural fibers have, after entering into the leakage path, firstly, the Modification of natural fibers make bridge on the micro cracks, then Elastic particles rapidly form thin film filter cakes at the function of the high viscosity structure of Nano polymer particles, thus enhancing the stratum’s ability of pressure bearing. This product has the characteristics of strong adhesion, high strength and small diameter size and etc, which is able to get into the rock pores and quickly form the chemical sealing layer with the effect of differential pressure, thus enhancing compression strength of stratum.