Shot peening is widely applied in the automotive and aerospace industries in order to improve the fatigue strength of the metal components by compressive residual stress. In the case of large components, the peening process is generally performed by moving peening equipment that follows a trajectory on the component surface by means of a robot. In order to construct a robot program for the shot peening of complex components, this study aimed to obtain a functional approximation of the impact pressure distribution in the shot stream. The impact pressure distributions were measured with pressure measurement films (Prescale) and a pressure distribution mapping system. The dependence of the mean impact pressure in the shot stream on the shot mass was in good agreement with the dependence of the arc height of the Almen strip on the shot mass. The impact pressure distributions using various shot masses and standoff distances were measured and approximated by modified Gaussian distribution functions, which included the saturation curve. Three coefficients in the modified Gaussian distribution functions depended on the shot mass and the standoff distance. The modified Gaussian distribution functions were used to determine the impact pressure distributions of a twice-shot peened samples. These calculated values were in good agreement with the experimental results. However, for tilted shot peening, the impact pressure distributions were more complex because the standoff distance at each position on the film was different. The impact pressure distributions of the tilted conditions calculated by the modified Gaussian distribution function, which considered the variation in the standoff distance, were in good agreement with the experimental results for a tilt angle ranging from 30° to 90°.