The nature of the mental representation during the mental rotation process is controversial. In our experiment, this issue was investigated by manipulating the integrity (reference lines) and complexity (square numbers) of the stimuli. The monotonic relation between transformation time and angular difference was found to be influenced by the integrity of the stimuli. As reference lines in a picture specified relative spatial relation among the picture’s components, when the space relation among a picture’s components was clear, participants did not rely on the ability of mental rotation to achieve this task. However, there were individual differences in the perception of spatial relations in the pictures. Nevertheless, the linear relationship was not modulated by stimulus complexity, which increased the overall reaction time. We inferred there are two subtle processes in the mental process of mental rotation – rotation of a reference line and reconstruction of the image. The degree to which participants relied on each process was accessed by the characteristics of the stimuli.