The initial development of the jet flow into superfluid helium (He II) bath was observed by particle image velocimetry (PIV), focusing on the flow structure and velocity field inside the jet flow, which could be the basis for the analysis of seeding process with a jet of particlecarrying fluid into He II, since it has decisive influence on the measurement accuracy. The He II bath had a temperature of 1.8 K, the polymer seeding particles had the diameter of 1.7μm, and the time span between two CCD pictures was 3 ms. The observed jet flow in He II had a parabolic flow pattern, similar to that in the normal fluid, however, the velocity field of jet flow was less uniform and regular than the normal fluid and much vortex flow was also found in some local areas. The amplitude of the oscillating velocity decreased along the progressive direction of jet flow and the mean velocity reached at about 2 mm/s after the flow left the nozzle for a distance of 35 mm.