We report a continuous phase transition between quantum-anomalous-Hall and trivial-insulator phases in a magnetic topological insulator upon magnetization rotation. The Hall conductivity transits from one plateau of quantized Hall conductivity e(2)/h to the other plateau of zero Hall conductivity. The transition curves taken at various temperatures cross almost at a single point, exemplifying the critical behavior of the transition. The slope of the transition curves follows a power-law temperature dependence with a critical exponent of 0.61. This suggests a common underlying origin in the plateau transitions between the quantum anomalous Hall and quantum Hall systems, which is a percolation of one-dimensional chiral edge channels.