A data processing system and an adjusting method thereof are disclosed. The data processing system includes a processor, a clock generator, a monitoring module and a determining module. When a target program is processed, the monitoring module monitors a first loading level of the processor, and transmits the first loading level to the determining module for recording. Furthermore, when a present program is processed, the monitoring module monitors a second loading level of the processor, and transmits the second loading level to the determining module. The determining module determines whether the second loading level matches with the first loading level within a preset period, and if it matches, the determining module generates and transmits a control signal to the clock generator, thereby making the clock generator generates a first clock signal to the processor, so as to increase the operating frequency of the processor.