中文摘要：

介绍了中国古代计时系统中的时间单位及其换算。详细讨论了宋代（宋代是中国古代科技文化发达的历史时期）对回归年等基本天文常数的测算和昼夜时刻的定授。结合宋代历法，分析宋代气朔、没灭、日出晨昏等各种时刻的计算方法。指出：在宋代中国已经建立了完整的时间系统，它包括定时授时系统、观象测时系统和历法计时系统。

英文摘要：

The time units and time units transformation in the ancient Chinese timing system are introduced. The measure and calculation of the basic astronomical constants such as the tropical year, and the determination and time service of the circadian time for the Song dynasty, which is an ancient historical period with flourishing science and culture, are discussed in detail. The calculation method of the time moment such as Qi, new-moon, mo and mie days, times of sunrise and twilight for the Song dynasty are analyzed combined with the calendars of the Song dynasty. Finally, it is pointed out that a complete time system, which comprises a time service system, an observations system for time measuring and a calendar system for time calculating, had been established in the Song dynasty.