To study the effect of laser flux on impulse coupling coefficient during laser aluminium target interaction at air ambient, by changing laser spot size on the target, the relationship between coupling coefficient and laser flux is achieved. The experimental results indicate that the coupling coefficient reaches to maximum when laser flux is 3.47×106 W/cm2, which agrees well with the theoretical result of 6.14×106 W/cm2. The two-dimensional model theory of laser supported detonation wave (LSDW) interacting with solid target is used to calculate the coupling coefficient. And the trends of theory and experiment are the same, but the two have prominent difference in values. The reason is that the laser spot is a little over large and the point blast model is not suitable to calculate the theory values.