As most of the traditional sensor devices consume large power in their standby stage, which is not an advantage for their long-term work, this paper designs an ultra-low power timing switch system, as a possible solution for such waste of power. The fundamental principle of this system is to control the power connection of the load by changing the state of the MOS switch in the system. Results obtained from the measurement structure for the system shows the current could be designed as low as 169.242nA, which indicates a great potential for ultra-low power applications. To verify its performance in engineering, a commercial hygrothermograph is modified by applying the as-designed ultra-low power timing system. Results indicate that the standby power consumption of the modified hygrothermograph is reduced to 3.54uW, which is 91.794 % lower as compared to the original mode.