The vertical density profiles of the gas-liquid mixture on the guide-sieve trays and normal sieve trays were measured through gamma ray absorption technique. The effects of factors on the mutual transition of different flow regimes were studied. It is found that inflection points of entrain-ment rate can be regarded as the criteria of transition of the flow regimes and the opretational range between two inflection points as being the transition regime. Mathematical correlations for tray hold-up(or clear liquid height)

average dispersion density and transition of flow regimes are given.