An expression of the distribution of load in the screw thread of a bolt-nut connection which is subjected not only to axial forces but also simultaneously to tangential forces and bending moments is obtained in the following process. First, let an expression of the distribution of load in a screw thread be a polynomial of turning angle (angle of rotation of point moving along the helix of the screw) as the variable with undetermined coefficients. Next, using the above expression, calculate the resultant axial force, resultant tangential force, bending moment at the bearing surface of the bolt head, deflection and deflection angle of the bolt as a distance from the bolt head. Then, decide the undermined coefficients in the postulated polynomial by means of the linear programming method, so that the results from the above calculation with this polynomial approach the experimental results as closely as possible.