中国计量科学研究院NIM4#冷原子喷泉钟自2003年8月起已经稳定运行6个月,并于2003年9～12月期间完成了系统频率偏差评定。文中介绍NIM4#钟的喷泉实验、微波频率锁定和对其主要频率特性的实验研究。实验和分析表明,NIM4#钟频率稳定性达8×10-13τ-1 2,复现性达5×10-15,频偏评定不确定度达8.5×10-15。作为旁证,NIM4#与中国计量科学研究院原子时TA(NIM)进行了120天比对,频率偏差在误差范围之内。 China Institute of Metrology NIM4 # cold atomic fountain clock since August 2003 has been stable operation of 6 months, and in September 2003 to December completed the system frequency deviation assessment. This paper introduces the fountain experiment of NIM4 # clock, microwave frequency locking and experimental study of its main frequency characteristics. Experiments and analysis show that the frequency stability of NIM4 # clock is 8 × 10-13τ-1 2, the reproducibility is 5 × 10-15, and the uncertainty of frequency offset estimation is 8.5 × 10-15. As a circumstantial evidence, NIM4 # was aligned with the National Institute of Metrology AT (NIM) for 120 days and the frequency deviation was within the error range.