The properties of small-x QCD are studied in this dissertation. One of the most interesting features of small-x physics is gluon saturation effect and to obtain direct evidence of this effect has been of great theoretical and experimental interest. We focus on deep inelastic scattering off heavy nucleus which may provide the first evidence of gluon saturation. Our results might be put into test in future by Electron-Ion Collider(EIC). We studied transverse momentum spectrum in gluon production and analyzed the result in different regimes of nuclear matter, dilute nucleus and saturated nucleus included. We first studied diffractive gluon production in small-x DIS, which itself is an excellent probe to detect gluon distribution inside nucleus. We then made an investigation on inclusive gluon production in DIS and, specifically, tried to understand the contribution from momentum conservation.