In order to solve the problem of the acoustic impedance mismatch between wood and air medium and the large attenuation of ultrasonic. These are the reasons that the signal-to-noise ratio of the detection signal is low and the measurement accuracy is not high. The phase coded pulse compression technology was applied to the air coupled ultrasonic detection of wood in this paper. Buck code sequence was selected as phase coding sequence, and the principle of generating and receiving signal demodulation of impulse compression excitation signal was detailed. The defect wood was used as the experimental object, and the difference of the detection signal between the defect and the non-defect was compared by single point scanning testing. Then the accuracy of wood defect detection was quantitatively analyzed by C-scan experiments. The results show that the signal-to-noise ratio of the detection signal is improved by 9. 12 dB when 13-bit buck code is used as the coding excitation signal, compared with sinusoidal excitation signal. The quantitative recognition accuracy of the defect for the node is 90% by C-scan results. The crack with width of 1 mm in the node can be detected effectively. These show that the application of pulse compression technology to the air coupled detection of wood can effectively improve the wood defect identification ability.