•Frost growth behavior at ultra-low temperature were investigated.•Three unique frosting phenomena were observed.•Frost growth mechanism was classified by frost surface temperature.•The effect of frosting factors on the frost growth behavior was investigated. An experiment was conducted to investigate the frost growth mechanism and its behavior under forced convection and ultra-low temperature (−160°C <Tw<−100°C) conditions. In ultra-low temperature frosting, peculiar phenomena such as formation of thread-shaped frost and a frost hill was observed. The point at which the frost growth mechanism changes was identified, and two stages of the frost growth mechanism were defined based on this point. The effect of cooling surface temperature, absolute humidity, air velocity, and air temperature on frost growth were investigated. As the cooling surface temperature decreased, the frost thickness increased, whereas the density was less affected. The results show that the frosting mechanism was dependent on the frost surface temperature, and it will be a useful guideline to solve the problems caused by frost generated under ultra-low temperature conditions.