This paper is focused on the method of ultra-high precision frequency measurement.Based on comparing the phase characteristic of standard frequency and measured frequency, it proposes the relationship between group phase-shift and quantitative phase-shift resolution when existing frequency drift. The relationship among measurement accuracy, trigger pulse position and the pulse number is set up when the measurement gate is formed according to the group period.Through the programmable counters,

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... e pulses of triggering gate are reduced. The application of nonlinear circuit compresses and expandes trigger pulse, which improves the accuracy of triggering gate. Frequency measurement system was designed using FPGA.Experiments showed that measurement accuracy can reach 10 -12 . The system can be used for ultra-high precision measurement of frequency .