Cycloidal rotor pumps are widely used in industries such as automotive and aerospace due to their advantages of compact structure, large displacement per unit volume, and low flow pulsation. With the development of new energy vehicles, rotor pumps are required to operate stably for extended periods under higher speeds, higher pressures, and harsher conditions, placing greater demands on their reliability. Addressing the specific problem of fracture failure of the inner rotor in a certain cycloidal rotor pump during bench testing, this paper first conducted a theoretical analysis of the inner rotor's metallographic structure. The metallographic results indicated that the inner rotor fracture was unrelated to material quality but was instead caused by the improper positioning of the slot on the pump's inner rotor, making the slot root the weakest part of the entire rotor material. Furthermore, sharp corners existed on the inner slot surface, leading to significant stress concentration at these locations. Subsequently, a finite element transient dynamics analysis of the cycloidal rotor pump was performed. The simulation results were consistent with the experimental findings, showing stress concentration occurring at the root of the inner rotor slot, with a maximum stress value of 1135 MPa, exceeding the material's yield strength. Therefore, by relocating the slot to avoid its root coinciding with the inner rotor tooth root and adding a fillet of R=0.5mm at the slot root to reduce the stress concentration factor, an improved design was proposed. Simulation results demonstrated that the maximum stress in the improved inner rotor design decreased to 863.2 MPa, a reduction of 23.95% compared to the original design, effectively resolving the stress concentration issue. Fatigue analysis software predicted the fatigue life increased to infinite life, verifying the effectiveness of the improvement.