Small signal stability is the ability to maintain stable operation of dynamic systems under small disturbance. VSC-HVDC network is the key to the interconnection of AC system, new energy and passive network. The small signal stability of VSC-HVDC network is directly related to the stable operation of the regional power system. This paper deduces the small signal mathematical models of voltage source converter, convertor controlling system and DC transmission network; verifies the correctness of the small signal model by the simulation comparison; lists the state matrix of VSC-HVDC based on state-space method; deduces the stability criterion of small signal through Lyapunov stability criterion and Participation factor matrix analysis method; demonstrates the applicability and accuracy of the small signal stability method by case analysis; provides the research foundation of controller design and decoupling mechanism for VSC-HVDC engineering application.