The main task of time keeping laboratory is to develop and maintain the national primary standard of Atomic Time Scale UTC (NIM), to participate in the TAI cooperation, to research on time and frequency transfer and measurement. At present the NIM clock ensemble consists of 13 Hydrogen Masers and 7 Cesium Clocks. The time difference between UTC (NIM) and UTC is kept within ±5ns. In 1995 NIM was appointed as one of the three G1 laboratories in APMP area which are responsible to calibrate G2 laboratories. The number of CMCs is 34 and is at top 2 in BIPM KCDB. “The new generation time and frequency primary standard key technique and application” project won the first prize of the National Science and Technology Progress in 2016.