The invention discloses a monitoring method and a device for subsidence of rock strata in an overlying bending and sinking zone of a goaf, and belongs to the field of coal mine disaster control and mining area environmental management. The method comprises the steps that a monitoring hole is formed until a bottom plate of the goaf from the ground; a steel base pile casing is arranged at the bottom of the monitoring hole, and anchored with surrounding rock by annular bulges under the action of a structural adhesive or cement mortar; a constant-speed subsidence layer pile casing, a slow-speed subsidence layer pile casing and a surface soil layer pile casing are embedded with the steel base pile casing layer by layer by sealing rings and balls, and anchored with the belonging layers by the annular bulges; subsidence values of the rock strata are read by a first fixing end, a first tape, a second fixing end and a second tape and by virtue of a ground tripod and turntable combination structure; and monitoring of the subsidence of the rock strata in the bending and sinking zone is achieved. The method and the device can continuously monitor subsidence development of the rock strata in the overlying bending and sinking zone of the goaf in real time and on a small scale, and have an important value in grasping an overlying rock stratum migration rule and a mining area subsidence rule under a mining influence.