To develop a suitable production process for fiber reinforced investment casting shell mold, three methods were studied: the traditional method (M1), the method of adding fiber into silica sol with mechanical stirring and ultrasonic agitation (M2), and the method of adding fiber into slurry with mechanical stirring and ultrasonic agitation for durations of 3, 15, 30, and 45 min (M3). The bending strength, high-temperature self-load deformation, and thermal conductivity of the shell molds were investigated. The results reveal that the enhancement of fiber dispersion through ultrasonic agitation improves the comprehensive performance of the shell molds. The maximum green bending strength of the shell mold by M2 reaches 3.29 MPa, which is 29% higher than that of the shell mold prepared by M1. Moreover, the high-temperature self-load deformation of the shell mold is reduced from 0.62% to 0.44%. In addition, simultaneous ultrasonic agitation and mechanical stirring effectively shorten the slurry preparation time while maintaining comparable levels of fiber dispersion. With the process M3-45 min, the fillers are uniformly dispersed in the slurry, and the fired bending strength and the high-temperature self-load deformation reach 6.25 MPa and 0.41%, respectively. Therefore, the proposed ultrasonic agitation route is promising for the fabrication of fiber-reinforced shell molds with excellent fibers dispersion.