Taking the spin-orbit coupling (SOC) into account, the lateral displacements (Goos-Hnchen shift, or GH shift) of ballistic electrons in a two-dimensional electron gas system modulated by ferromagnetic stripe and external voltage is investigated. Spin separation is realized by the GH shift, which provide theoretical foundation for designing spin separation devices. The conclusions are as follows. These anomalous lateral displacements can be tuned effectively by adjusting the incidence angles, magnetic strength of ferromagnetic stripe and Rashba SOC coefficient. It is shown that the lateral displacements can be negative as well as positive. The displacements are related to the spin polarization, which can be used to separate the different spin-polarization electrons. Based on these phenomena, a kind of spatial spin beam splitting of ballistic electrons by the displacements is proposed. The results are beneficial in designing some spintronics devices.