Abstract: Bend shaft is the main drive part，its mode character impacts the pump′s mechanical behavior and efficiency.Based on the finite element method and modern CAE software，the authors of this paper calculate top 30 natural frequency of a five-piston injection pump bend shaft′s and analyze its mode characteristics，some mode shapes are presented.By calculating，it is found that the bent shaft natural frequency is intensive at low-level frequency segment，there are only two available frequency interval，the current excitation frequency is in the mode frequency interval[15，16]，the other available frequency interval is fixed frequency interval[23，24].These two available frequency intervals do not meet engineering standards commendably.So input speed fluctuations and output load fluctuations should be strictly controlled when injection pump works to avoid sympathetic vibration，which can lead to internal component failure.

Key words: mode analysis, bent shaft, water injection pump, excitation frequency