A new method to measure the refractive index and the inclination of the sample in collection-mode scanning near-field optical microscope is presented.In this method,the illumination intensity is controlled by a feedback loop,the vertical vibrating tip scans the sample with a constant distance and the sample is illuminated by two symmetry light beams.Altering of the illumination intensity and the sampling of the local intensity are controlled by digital signal processing to be synchronized with the vibration of the tip.A group of extreme values of the tunneling light are obtained in one oscillation period.In another oscillation period,changing of any illumination beam will modify the near field distribution.Then,another group of extreme values of the tunneling light will be obtained.The refractive index and the angle of inclination of the object can be computed from groups of extreme values that obtained from multi-oscillation periods.Grating as well as erythrocytes membrane was analyzed in our experiment.Topography images of the grating produced by our prototype instrument are shown to have a lateral resolution better than 400 nm.As for the erythrocytes membranes,the refractive index of it is about 1.4.It can be concluded that this method could not only measure samples′ refractive index effectively but also offer a new approach to rebuild samples′ topography image using optical information.