Abstract: Weizhou11-1 oilfield,lying in Beibu Gulf Basin in west area of South China Sea,where sidewall instability problem is easier to appear in drilling process,bringing very big risk for drilling process.Therefore,research on sidewall stability mechanism for this oilfield is very necessary.With the results of research on sidewall stability in Weixinan oilfield group,this paper systematically summarizes sidewall stability mechanism and some specific conclusions on WZ11-1 oilfield,including micro-crack status,the size and direction of Earth stress,formation collapse pressure profile following borehole trajectory.Then it proposes corresponding practical technique strategies,mainly including confirming reasonable drilling fluid density,applying high strength anti-collapse oil-base drilling fluid,optimizing borehole trajectory,decreasing the exposure time of open-hole interval and so on.It made good results by applying the said techniques in drilling process of complex formation in Weizhou11-1 oilfield,no complicated cases and accidents caused by sidewall instability happening during the drilling progress in WZ11-1 oilfield.