HVDC breaker is an important device for realizing DC networking. Taking ±535 kV hybrid DC breaker of Zhangbei HVDC grid project as the research object，its insulation structure is mainly analyzed and designed in this paper. The trend of voltage distribution for the DC breaker is calculated with wide-band circuit model by PSCAD. Combined with the overall insulation requirements of the DC breaker，the withstand voltage levels for the key components are proposed. Based on the overall layout of the DC breaker，the equipotential design and insulation coordination are carried out，considering the operating environment，voltage waveforms and electrode types. Under typical operating conditions，the electric field distribution of the whole three-dimension DC breaker is calculated and evaluated by the finite element simulation software. The insulation tests of the DC breaker are carried out. Through the research of this paper，one suitable design method for the insulation structure of DC breaker is proposed，which is modular，sub-regional，layered and single-point nearby potential fixed. The maximum electric field strength on the surface of DC breaker fittings is 27.7 kV/cm under the lightning impulse withstand voltage，and 19 kV/cm during the fault current breaking process. No flashover or breakdown occurs during the type tests，satisfying the requirements of engineering applications. The research results can provide reference for the insulation structure design of high-voltage equipment.