In this paper phase space reconstruction technique is used for distinguishing the combustion states in the boiler furnace. The phase space maps and the correlation dimensions under the stable combustion & the unstable combusition are charted and calculated. The simulation and calculation results of the actual flame signals show that the phase space maps and the correlation dimensions under both combustion states are different at all time. Therefore it is presented that the correlation dimension ought to be regarded as the characteristic parameter to distinguish the combustion states of the flame in the boiler furnace. And the approach presented in this paper may be applied to develop the novel optical flame detector.