Abstract: Some instability analyses were carried out according to the experimental results of primary breakup of symmetrical spray of water and anhydrous-ethanol.It is shown that the process of primary breakup can be divided into two stages in the experimental condition: the first stage is the nonlinear development of liquid instability and the stretch of spike to form a jet caused by inertia force and resistance force of air; the second stage is the process of breakup to liquid bead cluster caused by jet instability. The analyzed result of droplet average diameter of primary breakup is approximate to the experimental result. According to the analyses, it is a necessity that the droplet average diameter of anhydrous-ethanol is smaller than one of water because the surface tension of anhydrous-ethanol is only one-third of the counterpart of water.