The characteristics of the purification of aluminum melt by flux injection technique with SDJ-1 flux and N-2 was analyzed through the experiments and the mechanism of improving degassing effect was investigated. By means of the study on the purification of several aluminum alloys, it is testified that the FI process has an advantage over purging techniques where an inert gas is bubbled through the melt or using flux alone. The FI process can reduce the hydrogen content to lower than 0.10ml/100gAl and increase the degassing efficiency. The reasons for the advantages of the purification by FI are studied in two aspects: mechanics and dynamics. From the view of mechanics, comparing the equation ( eta < (K)/(V)) with the induced equation( eta < (3alpha)/(3V)),it is concluded that the condition (a > K)is very important in removing inclusions from the melt. Furthermore the refining temperature is located on account of the relations between eta and t. From the view of dynamics, the term "channel" is proposed to explain the advantages of the process based on the reaction between inclusions and hydrogen: the flux and the oxides form many narrow channels, which absorb hydrogen and make hydrogen collect around them easily. The channels indirectly increase the contact area of bubbles with the melt when the bubbles go though the channels and at the same time increase the difference of partial pressure of hydrogen between the two sides of the interface. Besides, by dispersing the bubbles through the melt diffusion distances are also reduced. As a result, the existence of the channels intensifies the parameters ((A)/(V) K t nu(h)) and makes for the purification, overcoming the defects of only using inert gas. Oxides and nitrogen have intimate contact with the melt and the bubbles help the flux go up quickly, which also is favorable to the purification. So the dynamical reason why the injection has higher efficiency than simply mixing the flux and gas is made clear. The discussion about the parameters in this paper is helpful to the practical production.