Jinshan is hydrocarbon accumulation area chiefly, which have complex lithology and mudstone development. With long soak time of drilling mud, problems of wall stability are projecting. Be based on layer physics and chemistry and mechanics stability analysis, scarce chemistry stability of drilling mud which cause wall instability. To heighten wall stability,Proposeing first opinion of plugging prevent caving.Prepareing prevent caving drilling mud. The system have sealing and restrain characteristics powerfully. High temperature and pressure filtration can attain eleven millilitre under. Sand bed intrude into two centimeter. Mud shale rate of recovery can attain ninetyfive percent above, effect of drilling mud prevent caving marked are remarkably.