At atmospheric pressure, the anode attachment can appear in two different modes: constricted and diffuse. In this paper, a magnetically rotating arc plasma generator is built to investigate dynamics of anode attachment. A constricted and diffuse anode attachment, as well as the transformation between the two modes, are obtained. Results show the constricted anode attachment to be preferable for low arc currents and a low magnetic field, whereas the diffuse anode attachment is favored by the opposite conditions. With an increase in arc currents/magnetic field, the constricted anode attachment can transfer from a restrike mode with high voltage fluctuation to a sliding mode with low voltagefluctuation and then to a diffuse anode attachment with a long arc-shaped structure. An expanding arc column and high-temperature anode are suggested as essential conditions for the diffuse anode attachment because a thinner and hotter anode boundary layer may be promoted. In addition, the time-resolved transformation of different modes exhibits a strong mutual influence between the arc column and anode attachment, which indicates complex coupling mechanisms exist in the near-anode region.