The pressure pulsations inner the hydraulic power pipelines not only deteriorate the precision of execution unit, but also bring on vibration, noise or other troubles in hydraulic device. In this paper, the output pressure pulsations were treaded as a stationary random process approximately. The mean square deviation of dynamic stress under the pumping source white noise exciting was calculated based on frequency responses. The first-passage failure criterion and fatigue damage accumulation failure criterion were adopted to analyze the dynamic pressure reliability respectively, and the relation of amplitude pulsations and the pipelines reliability was obtained. The results indicated that the preventative design method of below10% of rated pressure did not meet the security specification of the hydraulic power unit.