The structure of flow field in plasma jet was investigated by means of electrostatic probes. Plasma jet was generated in plasma torch with dc electric arc stabilized by water vortex. The generated plasma is characterized by very high temperature and velocity and low density. An array of several electric probes was moved across the jet in various axial positions. The lines of the same probe current were evaluated from the measured signals. These lines represent the lines of the same plasma properties. The process of entrainment of ambient cold gas at the jet boundary and production of separated plasma eddies surrounded by cold gas was visualized by the applied method. Characteristic dimensions of jet structures and their velocity were determined.