Addressing the limitations of the traditional energy system in effectively dampening source-load variations and managing high scheduling costs amidst heightened renewable energy penetration, this study proposes a bi-level optimal scheduling model for an integrated wind-solar-hydro-thermal and energy storage integrated energy system considering the quasi-line demand response. Firstly, several typical load pre-alignment lines are constructed by clustering and scenario reduction. Then, a hierarchical optimization strategy is designed considering the difficulty of model solution, system economic benefit and source-load coordination. The upper layer decides the start-stop plan of thermal power units, and the lower layer optimizes the total operation cost of the system and the total output variance of thermal power units. Secondly, consider the quasi-linear DR to further optimize the model; finally, through the simulation experiment of IEEE-26 system, the results show that the scheduling strategy successfully suppress the fluctuation of new energy output, reduce the system operation cost and reduce the frequent start-stop and adjustment of thermal power units. In addition, the introduction of quasi-linear DR can further optimize the scheduling results, so that the system operation cost and thermal power output variance are reduced by 5.41% and 43.05% respectively.