The downhole liquid atomization by supersonic nozzle is an economic and efficient way to alleviate the liquid loading, but the optimal efficiency conditions are still not clear. In this paper, experimental studies were conducted in a 6-m long and 30-mm inner diameter vertical Perspex pipe to evaluate the performance of supersonic nozzle in different conditions. Camera was employed to record the characteristic of fluid flow downstream the nozzle, and the MATLAB was used in combination with DIP-image technology to determine the diameter of droplets. The experimental results show that mist is easy to be captured by the liquid bulk due to the liquid loading downstream the nozzle when the gas-liquid two phase flow pattern downstream nozzle is non-annular flow, thus leading to a failure of this technology. Due to the huge temperature drop in the annular flow condition, small fraction of mist is condensed into droplets and then attaches onto the pipe wall, forming liquid film. The remaining mist can still flow upwards. In this article, when the gas velocities upstream the nozzle range from 2.4m/s to 3.2m/s, the size of droplets range from 50μm to 1000μm correspondingly. Field application indicates that this technology under the effective operating envelops are able to be efficient to remove the liquid-loading, and the gas wells can maintain a long-term stable production.