We propose a photonics method of measuring microwave frequency based on photonic mixing.In this approach,a tunable microwave delay line (TMDL) is utilized to control the time delay between radio-frequency (RF) path and optica l path. By employing two cascaded Mach-Zehnder modulators to realize photonic mixing,w e can establish the relationship between microwave frequency and direct current (D C) optical power,and also our system has the advantage in reducing cost.After simul at ing and analyzing the established theory model,we can design the time delay betw een RF path and optical path,so that the system frequency measurement range will be optimized.The simulation results show that it is suitable for the frequency ran ge of 1－6GHz to select the time delay Δτ₁ between optic al path and RF path 1around 15ps,and the time delay Δτ between the two RF pat hs around 20ps.In the experiment,a vector network analyzer is utilized to measure the time delay,we got Δτ₁ as 17.7ps,Δτ as 16.9ps,and then the measured f requency range of 1to 6GHz with a measurement error less than ±0.2GHz is demonstrated experimental ly. The source of the measurement error is mainly from the phase measurement uncertainty of the vector network analyzer and the power fluctuation of the las er.The measurement accuracy can be improved by taking appropriate measures.This method can provide a low cost photonics solution for microwave frequency measurement.