Abstract: The purpose of the paper is to introduce a coherence extender and the experimental study of the device.The extender is slanting Fabry-Perot etalon.used in the resonator of the domestic argon-ion laser.With the coherence extender,the co-herence length of argon-ion laser can come from 5cm up to several meters and the power loss is the range of 25%～40%, The device can be used in the field of coherence detection.