The invention relates to an anti-foaming method in foam drill, belonging to the oil drilling field. In the method solid phase, partial air phase and partial liquid phase can be separated by first-order cyclone separator. Not-separated foam enters into second-order anti-foaming centrifugal machine to separate air phase and liquid phase fully. The method can eliminate foam effectively in foam drilling process so that drilling matrix liquid can be used repeatedly. It is provided with convenient method, small cubage of anti-foaming device, light weight, few assistant equipment, low failure rate, decreased drilling cost and decreased circumstance pollution so on.