In this research, micro-nano bubbles formation inside the venturi tube has been investigated using image processing technique and high-speed photography. For the purpose, two models of venturi tubes with different dimensions were made of light and transparent plexiglass and then they were tested with various water flow discharges. After the injection of air into the venturi tube, a high-speed camera has been used to capture images of two-phase flows passing through the venturi tube. The captured images were processed by MATLAB software. After investigating the results and obtaining the average diameter of the bubbles, the number of Micro-Nano bubbles and the velocity in the center of venturi tube have been calculated and the related graphs have been analyzed. The results show that reducing bottleneck length and increasing flow discharge inside the venturi tube lead to the formation of smaller bubbles and the number of Micro-Nano bubble increases.