The subpeak was first observed in glassy Fe-Al ribbons. The origin of the subpeak is not due to the system size, but it is consequence of the Occurrence of local atomic structural order. The usual stability of undercooled liquids against crystallization is explained by means of local atomic structural order. Direct experiment shows a correlation between the nucleation barrier and intermediate-range order with decreasing temperature in an Fe-Al liquid. A corresponding simulation is used to observe the formation of the subpeak in a liquid system directly.