The unstable-resonator spatially enhanced detection (USED) coherent antistokes Raman scattering (CARS) measurement of temperature in CH4/air flame is reported. The USED CARS measurement system which has a high spatial solution of ～0.1 mm in diameter and ～3 mm in length is constructed and permits instantaneous thermometry at a 10 Hz rate. The single-pulse N2 Q-branch CARS spectra have been obtained from CH4/air flame and the CARS data are analyzed by comparison with theoretical spectra generated at various temperature. The temperature distribution of CH4/air flame have been measured by broad-band USED CARS and the measurement results have been analyzed. The uncertainty of single-pulse temperature measurement is less than 5% for T=2038 K.