For machined parts, the surface roughness and profile would have a significant impact on the fatigue life and fracture mechanism. At present, a lot of research have been carried out on the cutting mechanism, modeling and machining performance of particle reinforced Al-based metal matrix composites. However, the study of fatigue life and fracture mechanism of machined parts after cutting particle reinforced Al-based metal matrix composites is rarely reported. In this paper, the fatigue life and fatigue fracture morphology of in-situ TiB2/7050Al MMCs were studied by high cycle fatigue test under different loading stresses. It was found that the surface roughness influenced the fatigue life greatly. With surface roughness decreasing, the fatigue life of machined parts increased exponentially. The fracture mechanism of cutting in-situ TiB2/7050Al MMCs was found to be brittle fracture due to the existence of fine particles. Besides, a fatigue life prediction model was established based on the machined surface roughness. With validation, the relative errors between prediction model and experiment were smaller than 11% indicating that the proposed fatigue life prediction model of machined in-situ TiB2/7050Al MMCs parts was of good reliability and accuracy.