Probe-assisted pulsed laser induced photo-detachment (LIPD) technique was usually used for diagnose negative ion denstiy,electronegativity and even negative ion temperature in the electronegative plasma.In our experiments,we have attempted to apply high energy pulsed laser beam with wavelength of 532nm to iradiate the capacitively coupled O2 plasma driven by 40.68MHz.Spatial potential of the plasma and electronegativity were diagnosed by exerting a certain positve bias on the probe aligned with laser beam at the center.