This paper presents a numerical simulation of the flow field on a one-dimensional pneumatic actuator. Unlike conventional actuators, this model uses dynamic pressure instead of friction to drive a slider. The objective of this simulation is to know the detail of the flow field under the slider as well as the influence of its levitation on the horizontal transportation. Secondary vortices to be formed under the slider may cause an instability of the slider movement. To further assure a stable transportation of the slider, absence of secondary vortices in the gap is desirable, which can be achieved by narrowing the gap width. However, a too narrow gap might cause a significant increase of flow impedance and thus sacrifice the horizontal transportation. Here, two cases with gap width of 100 and 50 μm were investigated. With a gap width of 50 μm, there was no secondary vortex formed; however, the horizontal transportation was greatly sacrificed. In contrast, with a gap width of 100 μm, there were formed several secondary vortices of a size one to two times the gap width. However, the horizontal driving force was about eight times larger than that in the case of a gap width of 50 μm.