A method for measuring the frequency stability of tunable laser is proposed by using confocal Fabry-Perot(F-P)interferometer.The F-P interferometer is used to get the output frequency of the laser as a reference,and the method eliminates the need of an independent optical source as a frequency reference.Using this technique,the frequency stability of the tunable external-cavity diode laser(ECDL)is measured to be 2.26×10~(-9)with an integration time of 20 ms. A method for measuring the frequency stability of tunable laser is proposed by using confocal Fabry-Perot (FP) interferometer is used to get the output frequency of the laser as a reference, and the method eliminates the need of an independent optical source as a frequency reference. Using this technique, the frequency stability of the tunable external-cavity diode laser (ECDL) is measured to be 2.26 × 10 -9 with an integration time of 20 ms.