Abstract: Stuck pipe are frequently encountered during well drilling and service.Free point back-off instrument is the most effective tool for detecting the exact free point and conducting explosion backing off afterwards.This instrument is a highly sensitive stress detecting device,which detects the deformation of the pipe string based on the piezomagnetic effect,while the deformation is converted into electric signals for identification,so as to determine the exact free point location.This method was introduced on many literatures,however,all of the free point back-off instruments used at home are imports from other country.There is not self-determination production at home.It particular introduced the study on this most effective tool,it also introduced the characteristics,innovation and application of this instrument.