According to the collapsing formation which is difficult to control the severe leakage and can not be effectively cemented, a new settable working fluid was developed. It is based on the conventional drilling fluid with good suspension capacity, rheological property, salt-resistant ability and good compatibility of drilling fluid, its suitable solidification intensity can be reached under certain conditions and can be used as sealing fluid or as cementing fluid in borehole instability formations to improve the sealing and cementing effect.