Abstract: Objective Compared with bogies suspended on the outer side of the axle box, built-in bogies offer advantages such as light weight, superior curve negotiation capability, lower wheel-rail wear and noise. However, built-in bogies typically suffer from insufficient primary lateral anti-rolling capability, very compact lateral dimensions, limited space for component arrangement, and lower adaptability to high-speed applications, making their use in high-speed EMUs（electric multiple units） relatively uncommon. In response, it is necessary to carry out research on the design and experimental verification of high-speed EMU built-in bogies. Method In the context of developing a new generation of high-speed EMU bogies, a new type of built-in bogie for 400 km/h high-speed EMUs is designed, utilizing composite plate spring technology and oil-gas suspension devices as primary suspension system. Strength simulation and analysis of major components are conducted using ANSYS and other software tools. SIMPACK multi-body dynamics software is used to perform dynamics simulation calculation of bogies. Fatigue tests of key components, rolling vibration tests on the bogie test bench, and full-vehicle track tests are also carried out. Result ＆ Conclusion The calculation and test results indicate that various technical indicators such as strength and dynamics performance all meet the requirements of relevant standards. Notably, the test bench trials achieved a speed of 606 km/h.