Disclosed are a method and apparatus for smoothing a link-line power of an electrothermal microgrid using a thermal storage heat pump cluster. The method includes: determining a current link-line power control target and pre-distributing a smoothing task to the heat pump cluster; making, by a heat pump start-stop control layer cluster, a heat pump cluster start-stop scheme, determining a start-stop state of the heat pump cluster and a start-stop smoothing component of the heat pump cluster according to the smoothing task, obtaining a remaining fluctuating power based on link-line fluctuating power and the start-stop smoothing component of the heat pump cluster; smoothing, by a heat pump cluster power adjustment layer, some medium and low frequency components and outputting a smoothing component of the heat pump cluster with respect to a storage battery output optimization target based on the remaining fluctuating power; and simultaneously undertaking, by the storage battery, a smoothing task of the remaining fluctuating power and outputting a storage battery smoothing component to complete the smoothing of the fluctuating power in a control cycle.