In electro-hydrostatic actuator (EHA) hydraulic systems, hydraulic pipelines are prone to flexural vibration under pump-induced excitation, which can compromise system stability and reliability. Addressing the mid-frequency broadband vibration reduction requirement in the 250-550 Hz range for EHA systems operating with variable motor speed, this paper presents a pipeline vibration reduction design and bandgap tuning method based on phononic crystal structures. The transfer matrix method is employed to analyze the band structures of Bragg-type and locally resonant-type phononic crystal pipelines, revealing the effects of geometric and material parameters on bandgap position and width. By utilizing the bandgap coupling phenomenon, a coupled phononic crystal pipeline is designed, and parameter optimization achieves a continuous coupled bandgap of 225-585 Hz, effectively broadening the bandwidth and covering the target frequency range that is difficult to achieve with a single phononic crystal structure. Finite element simulations further verify the vibration attenuation performance within the target frequency range, demonstrating an average vibration transmission loss of 50.24 dB.