Abstract: Induced fracture lost circulation during the drilling process is a common type of lost circulation，the key to control it is to stop the propagation of the fracture.Aided by the rock fracture mechanics，the mechanism of preventing an induced fracture from propagating was proposed.On the basis of analyzing the pressure distribution in the facture after plugging，the viewpoint that the support stress of the plug in the induced fracture should be equal to the drilling fluid′s pressure is presented.The fracture mechanics model and the formula for calculating are developed.The effect of blocking location on preventing the extension of an induced fracture was studied，the results demonstrated that the best type of plugging location is certain distance near the facture mouth；the evaluation device must reflect this plugging location form.The requirements of preventing the induced fracture are presented，that′s to say the fluid′s pressure in the isolated fracture tip part must be lower than the horizontal minimum principal stress，it will help stop the propagation of the induced fracture to accelerate the pressure drop.

Key words: lost circulation, lost circulation control, induced fracture, stress intensive factor, plugging location 