Abstract: A modularized small signal modelling method for DC grid was proposed. A DC grid is divided into AC network subsystems, converter subsystems and the DC network subsystem, where each converter subsystem is further divided into AC electrical module, DC electrical module, controller module, signal filtering module and phase lock loop module. Models of each subsystem and each module are interlinked through linking matrixes to form the overall small signal model of a DC grid. Small signal model of each module and the linking matrixes between different modules were derived. A generic control model based on control flag was proposed to model different typical VSC controllers using a same modelling structure. Linking matrixes between DC network and the converter systems were derived, an overall modelling matrix for DC grid was then presented. Accuracy of the proposed modelling method was verified on a 3-terminal HVDC system. Results show that for small disturbance, the small signal model is able to output almost identical simulation results as detailed electromagnetic model and nonlinear state-space model. The proposed modular modelling method and generic controller modelling method is able to significantly reduce the complexity of small signal modelling of DC grids.