Abstract: Chain circuit static synchronous compensator（STATCOM） has significant advantages,such as easy to achieve split-control,simple to implement modular design,high reliability,good harmonic characteristics,no multi-transformer and no series connected power semiconductor devices,having been widely studied in improving system transient stability,system dynamic performance and customer power quality.Its mathematical model is the key to studying the corresponding control strategy and analyzing dynamic performance.This paper began with dynamics models of single-phase H-bridge,modeling of single-phase chain circuit STATCOM was studied,switching cycle average model and small signal AC model of single-phase chain circuit STATCOM were established.The simulation results verify the correctness and validity of the models,and the models can lay theoretical foundation for equipment-level control strategy study.