This paper studies formation control of a group of unicycles, and proposes a distributed control law, depending only on the relative position and bearing angle of one nearby vehicle, to realize the circular formation and render more achievable general formations by designing the parameters in the control law. For circular formation, not only we can strictly prove that only two sets of equilibria are asymptotically stable, but also by choosing appropriate control parameters, determine the distances of two vehicles and the radius of the circle that all the unicycles converge to.