Spray forming is an advanced technology that is used to produce a variety of high—performance materials with the characteristics of rapid solidification. By properly controlling of spray forming parameters, it is possible to fabricate near—net—shaped preforms, such as rod—billets, strips, and tubes. During the billet spray forming process, the shape of deposit strongly influences the solidification and consequently end—product quality. Therefore, it is necessary to reveal the shape forming mechanism in spray forming process. In the present work, a three—dimensional (3D) model, tracing the coordinates of the moving surface of a growing spray—formed billet, has been formulated to predict the shape evolution of the general deposit. This geometric model takes into account geometrical process parameters in the whole spray forming process: mass flux and mass distribution, position of the atomizer, distance between atomizer and the preform, substrate withdrawal velocity and rotation speed. This makes it possible to model not only the growth of a Gaussian shaped deposit in which case the spray axis and the rotation axis coincide, but also the profile evolution as there is a spray angle between these two axes. For this purpose, “shadowing effect” must be taken into account as a core part of the surface evolution algorithm. On the basis of this 3D model, a timesaving and accurate methodology is established to determine the shadowing effect coefficient, using the “triangular element checking” algorithm coupled with back face culling (BFC). The transient shape modeling has been validated by numerical algorithms and experimental investigation, and has proved that the simulated billet profiles are in good agreement with the experimental data. The effect of spray forming parameters, such as spray distribution parameters, withdrawal velocity, initial eccentric distance, spray angle and angular velocity of rotation, are analyzed. According to the obtained simulation results, the most dominant parameters affecting the shape evolution of deposit are the spray distribution parameters, withdrawal velocity, and initial eccentric distance. It is also found that the spray angle mainly affects the profile  of the top transition region of the rod. The effect of the angular velocities of substrate on the shape evolution of the deposit is not significant. Finally, the maximum withdrawal velocity and maximum initial eccentric distance are deduced based on the analysis of shape form mechanism, which can be used to guide the process optimization during spray forming.