Abstract: The shell of a 63CY-104 type swash plate piston pump often cracked, causing hydraulic oil leakage. Through metallographic inspection, fracture analysis and finite element analysis, the reasons for the cracking of piston pump shell were analyzed. The results showed that the straight, thick and sharp C-shaped graphite at both ends in the plunger pump shell structure was the main reason for cracking of shell. The plunger pump was subject to greater vibration during operation, and the 3rd, 4th, and 5th modes of shell changed greatly, which was prone to resonance and caused cracks in the shell.