Water electrospray in the cone jet mode was performed by a polymer micro-atomizer. A high aspect ratio dielectric polymer micro-nozzle and an in-plane extractor were proposed to concentrate the electric field at the tip of the micro-nozzle, which prevent electrical discharge caused by the high surface tension of water. The effect of the in-plane extractor was confirmed by electric field simulation and electrospray experiment. A micro-pillar array was also proposed to prevent surface wetting of the polymer micro-atomizer during the electrospray. Water electrospray of the polymer micro-atomizer was operated in a flow rate of 0.15-0.30 ml/h with a voltage of 1.5-3.0 kV, -2.0 kV, and -4.0 kV at water, a guide ring, and a collector, respectively. The key features of the cone jet mode such as Taylor cone, jet, and water micro-droplets were visualized by using nanosecond pulsed laser illumination.