In a linear pinch, the configuration of a plasma surrounded by a constant-pitch field is produced by the appropriate choice of a start-timing between θ-pinch and z-pinch. The magnetohydro-dynamic stability of the screw pinch plasma is investigated by the magnetic probe, loops and so on. The growth rates of a m=1 kink instability are evaluated from the experimental data. It is seen that the experimental values are lower by about two times than those predicted by the sharp boundary magnetohydro-dynamic theory.