The front of the Zoulang Nanshan Caledonian volcanic island arc zone in the northern Qilian Mountains is a forearc accretionary terrane, composed of multiple accretionary volcanic island arcs, flysch accretionary wedges,high-pressure metamorphosed detachment zones and remnants of ophiolites. It resulted from the northeastward subduction of the Early Palaeozoic Qilan oceanic crust beneath the Alxa block. High-pressure metamorphism, which occurred during the subduction, progressed through three stages: the initial stage of medium T-high P,the main stage of temperature decrease and pressure increase, and the lag stage of pressure decrease and temperature increase. Finally the paper presents a retrotrench subduction dynamic model indicative of northward subduction of the central Qilian block and southward accretion of the Alxa block during the period of 450-500 Ma.