Abstract：“The device of dynamic measurement with point position in Concealed work”was developed to measure it. The principle of communicating vessels was used in this machine; observation roadway is not necessary to be built. Combined with the environmental conditions in a mining area,the measurement errors produced in application were regarded. They included the liquid inflation caused by temperature measuring in goaf and observation tube liquid evaporation. The results show that the errors can be controlled between 3 and4 mm in a goaf area with no spontaneous combustion tendency. Thusly,the instrument can be undertaken the field measurement about floor deflection value in a goaf.

Keyword：goaf;bottom rock;floor heave value;