Laser optical pumping of caesium atoms in a high magnetic field of 1.514 T is reported. Steady absorption spectra from hyperfine Zeeman sublevels are obtained with two semiconductor lasers. The populations in different hyperfine Zeeman sublevels show unusual changes when the power of the pumping laser is changed. The optical pumping and the spin flip by hyperfine interaction bring about the marching of atoms from the lowest to the highest M(I) sublevels of the ground state.