The invention discloses a flexible connection method for a crosshead to a piston of a well drilling pump. According to the flexible connection method, any one of three rigid and fixed connection positions, which are formed by the crosshead, a middle pull rod, a piston rod and the piston in sequence, is connected by adopting a hinging manner of a spherical hinge; the other two positions are connected by adopting a previous rigid connection manner. According to the method, a spherical hinge structure allows a connected piece to do any deflection movement in X, Y and Z directions, so that manufacturing and installation errors are automatically compensated, and the eccentric wearing problem of a cylinder sleeve piston caused by the abrasion of a guide plate and the like is avoided; the service life of the cylinder sleeve piston is prolonged, and the product quality of the well drilling pump and the working efficiency of well drilling work are greatly improved.