The Portevin-Le Chatelier (PLC) effect associated with avalanching shearing deformation, will occur during a tensile test for many alloy materials. With the aid of the digital speckle metrology technique including digital speckle pattern interferometry (DSPI) and digital speckle correlation(DSC), an optical system was set up to measure the three-dimensional deformation on the specimen in real time during tensile test. The nucleation process of a shearing band in Al-Cu polycrystal was captured by using a high-speed digital photography (1000 frame/s). The quantitative results of the displacement field and axial strain field on the front and lateral surface are obtained by digital speckle correlation method and the propagation of the out-plane deformation of the band is vividly visualized by correlation fringes. By combining the in-plane and out-plane deformation results, a report of three-dimensional nucleation process for the shearing band is presented here.