Abstract: In order to study the relationship between micro-pore throat characteristics and physical property difference, drill core samples of extra-ultra low permeability sandstone from a reservoir in the Yanchang group of the Ordos Basin were selected for physical property analysis, cast section, SEM and mercury penetration techniques. The results indicate that throat type in an extra-ultra low permeability sandstone reservoir is versatile and minute. The content of major throat which makes a dominant contribution to permeability is low, which is the main reason for poor physical property. Meanwhile, micro-cracks aggravate the difference in physical property. The distribution and variation coefficients range from 2.0 to 3.0 and 0.15 to 0.3 respectively, providing a major contribution to the permeability of sandstone. Physical property is the combined result of the mutual effect of multiple factors. Permeability presents large deviation when the reservoir space is composed of different pore throat types.