The generation of nanobubbles (NBs) by replacing different dissolved gas solutions has been widely adopted. Recently, we have found that mixing solutions with different gas contents can also produce a large number of NBs. However, the mechanism of the formation of NBs during mixing has not been well explored. Here, we designed a series of experiments to investigate the influence of mixing of different solutions on the concentration and size contribution of formed NBs via the help of nanoparticle track analysis. The effect of nanosolids was also investigated. The pressurization and depressurization were used to produce NBs. The results indicated that NBs can be influenced by the gas contents and nanosolids. The addition of nanosolids is beneficial to produce more NBs. Both the nanosolids and gas contents together are expected to substantially increase the concentration of NBs. These results will be very helpful to understand the formation and stability of NBs.