Based on the third-order aberration theory,a design method is put forward for beam expander that the aberration of an object lens and an eyepiece are conjugated,a beam expander with aspheric is designed and made up of two lens. The result of design shows that aberration of system is well corrected. In order to test the beam divergence angle for 1.064 μm invisible wavelength,the method is put forward for testing of beam divergence angle with linear CCD and oscillograph,this testing method is handy and easy to be realized,and testing precision is high.