Silicon carbide (SiC) particle-reinforced aluminum matrix (SiCp/Al) composites have continuously increased applications in abundant industries due to their superior mechanical properties. However, such composites have issues achieving desired machinability and quality standard due to the presence of SiC particles which is the main hindrance to their applications. In this paper, the methodology of ultrasonic vibration-assisted helical grinding (UVHG) of SiCp/Al composites has been applied to achieve to desired quality and efficiency for such composites. Then a mechanical cutting force model was developed to predict grinding forces. The grinding force was separated into friction force, plastic deformation force, and fracture force on account of the material removal mechanism. The undeformed chip thickness and cross-sectional area were calculated for the grinding force of a single diamond abrasive grit and then extended to the whole tool. By considering the acoustic softening effect of reduction of deformation stress caused by ultrasonic vibration, the acoustic softening coefficient was first proposed in the model to correct the impact of the ultrasonic vibration for properties of SiCp/Al composites. The experimental machining (UVHG) was carried out considering the different groups of experiments. The experimental results found agreed with the predicted values of cutting forces. The prediction deviation of the model was 7.06%, which could provide further guidance for the grinding process optimization of SiCp/Al composites. The novel cutting force predicted model and proposed machining methodology could be applied to machining SiCp/Al composites at the industry level and further research work.