Liquid-liquid phase separation (LLPS) in the rapidly solidified Fe71Cu10P10B9 alloy under different casting conditions is investigated based on the XRD, DSC, and SEM measurements. It is found that during rapid solidification process, Cu-rich globules precipitated in the matrix which mainly consists of α-Fe and Fe3B0.82P0.18 crystals. With increasing cooling rate, LLPS becomes weaker, leading to less precipitation of Cu-rich globules, while the microstructure of the matrix became finer. Magnetic measurements show that the saturation induction and the coercivity of the present samples increase first and then decrease with increasing cooling rate. The corresponding mechanisms related to magnetic performance are also discussed details.