Abstract: The chain instability of residual coal pillars in the goaf shows obvious linkage-induced disaster effects. Using the key pillar theory of residual coal pillars’ chain instability, the technical method for rock strata control of pillar-side backfilling is firstly proposed in this paper. Then, the core mechanism of pillar-side backfilling rock strata control method is revealed. And the material, strength, width and shape of pillar-side backfilling body are determined in the rock strata control method. The rock strata control effect of pillar-side backfilling method is also evaluated. The potential application range and fields of pillar-side backfilling rock strata control theory are lastly prospected. The research results show that: (1) The pillar-side backfilling rock strata control method is conducted by implementing the double pillar-side full backfilling, double pillar-side partial backfilling, single pillar-side full backfilling, or single pillar-side partial backfilling. The newborn pillar-side backfilling body plays a side protection role for the key pillar, which can also form a coordinated load-bearing structure with the key pillar. The rock strata movement can be effectivele controled. It can also guarantee the safe, efficient and green mining of coal resources. (2) The rock strata control core mechanism of pillar-side backfilling method is mainly embodied in four aspects: ① The coupled bearing role is played by the key pillar and the pillar-side backfilling body. ② The pillar-side backfilling body produces lateral restraint on the key pillar. ③ The stress strengthening is shown for the key pillar after the pillar-side backfilling. ④ The long-term deterioration of the key pillar is reduced. (3) The returning solid waste backfilling material and in-situ solid waste backfilling material can be seleled in the pillar-side backfilling rock strata control method. The ultimate compressive strength of pillar-side backfilling body should be greater than or equal to the transferred load. The width of yield zone in the coupling bearing body of pillar-side backfilling body and key pillar cannot be extended to the original elastic core area of key pillar. The shape of the pillar-side backfilling body mainly includes rectangular, ladder, stepped and multi-stepped ladder types. The stress concentration of key pillar will be reduced after pillar-side backfilling. The width of plastic zone will reduce on the both sides of key pillar, and the width of elastic core area in the central area will increase. The distribution characteristics of stress and elastic core area indicate that the rock strata control effect of pillar-side backfilling is good. The fundamental theory for rock strata control of pillar-side backfilling can not only be used for the prevention and control of chain instability of residual coal pillars, but also be applied to technical fields such as the re-mining of high-quality residual coal resources as well as the maintenance and utilization of underground space. It can also be applied to the non-coal resources mining area. The proposal of the basic theory for rock strata control of pillar-side backfilling can promote the development of green mining theory and technology in China.