Experiments on electro-spraying were carried out under a combined electric field based on micro-scale combustion system by using ethanol as fuel. A stable cone-jet mode was obtained. And theoretical calculation was performed based on the cone-jet mode. The distribution of electric field strength was calculated by using ellipse integral method and the relationship between Cartesian coordinates and polar coordinates. The results showed that the electric field strength produced by the ring electrode alone at the center of nozzle reached its maximum value, which was 0 V/m at the position of the center of ring electrode. It increased with the increase of cone angle when all the other conditions were kept the same. The electric field strength produced by the ring electrode could be ignored compared with that produced by the nozzle electrode due to the much bigger diameter of ring electrode and smaller electrode spacing. The distribution of electric field strength in the jet region was axis-symmetry and extremely non-uniform in the angle range φ of 0°~49.3°. The strength in the center of nozzle was very small while it was bigger around the outer side of nozzle, which enhanced the electric induction. Changing the voltage of the ring electrode put little effect on the electric field distribution in the jet region, but the electric field strength in the spraying region was greatly increased.