Abstract: The theory of light force and the basic notions of atom cooling and trapping are discussed.The techrigue is by using a magnetic field gradient produced by a quadrupole field and three pairs of circularly polarized,counterpropagating optical beams.Then the atoms in the trap will be cooled by a dissipative force,and will be trapped in the center of the trap by a restoring force.The methods make it possible to realize BEC (Bose Einstein Condensate).