Abstract: The accurate establishment of in-situ stress model is an important basis for oil and gas exploration and development. The constraint analysis method is used to establish in-situ stress model, whose essence is to analyze the constraint boundaries of vertical principle stress, the max. horizontal principle stress and the min. horizontal principle stress, narrow the computing boundaries and improve computing accuracy. On the basis of the fault pattern theory proposed by E. M. Anderson, 4 types of in-situ stress boundaries and the corresponding constraint equations are obtained. The frictional strength on the original fault surface determines the upper limit of stress differences between the max. and min. horizontal principle stress; formation pore pressure can give the lower limit of the min. horizontal principle stress; the width of borehole breakout or drilling-induced fractures can be used to determine the upper limit of the max. horizontal principle stress; the min. horizontal principle stress can be measured by hydraulic fracturing tests and the max. horizontal principle stress can be estimated as well; the vertical principle stress can be gained through density logging curve integral. The actual application shows that the constraint analysis method is an effective way to establish in-situ stress model and to determine the 3 principle stresses (especially the max. horizontal principle stress) combined with the results from laboratory stress experiments