To analyze the process of hand-timing and the resulting data collected from the hand-timing computer system(HTCS),including the timing operator′s reaction times of starting and stopping the watch,the results from the timing,the simulated electronic timing,the major factor that affects the time-keeper′s accuracy of time-keeping were studied,i.e.the stability of the timekeeper′s reaction time,rather than the time-keeper′s reation time.The leading cause that inflicts error between the hand-time-keeping and the electrionic time-keeping consists in the pitfall that the time-keeper makes a wrong judgment in stopping the watch.The analytical results provide theoretic gist for the selection and training of time-keeping operators. To analyze the process of hand-timing and the resulting data collected from the hand-timing computer system (HTCS), including the timing operator’s reaction times of starting and stopping the watch, the results from the timing, the simulated electronic timing, the major factor that affects the time-keeper’s accuracy of time-keeping were studied, iethe stability of the timekeeper’s reaction time, rather than the time-keeper’s reation time. The leading cause that inflicts error between the hand -time-keeping and the electrionic time-keeping consists in the pitfall that the time-keeper makes a wrong judgment in stopping the watch. The analytical results provide theoretic gist for the selection and training of time-keeping operators.