Abstract: According to theoretical prediction, the distribution of acoustic wave power flux launched in both directions by the linear FM interdigital transducer （IDT） is asymmetrical in nature. Methods of acoustooptic diffraction have been employed to detect acoustic field distribution of linear FM IDT. Three unapodized linear FM IDT which have different parameters are examinted. These transducers are formed with aluminum electrodes deposited on the ipieroelectric substrates of Y-cut Z-propa gating lithium niobate. Experimental results show that the surface acoustic wave （SAW） power flux radiated from the high frequency port of linear FM interdigital transducer is found to be stronger than that from the low frequency one. The asymmetry increases with the number of the effective finger pairs. In general, the asymmetry increases as the exeited frequency increases but the relation between them is not monotonic. Using the equivalent crcuit model, numerical evaluations of the asymmetric distribution have been made. The theortical curves essentially agreen with the experimental results.