The invention discloses a small sand body boundary identification method and a small sand body space quantitative description method. The small sand body boundary identification method comprises the following steps: summarizing the development rules and scale of a sand body according to the geological situation of a region; summarizing the seismic response characteristics of a reservoir and carrying out seismic profile identification and interpretation through seismic forward modeling; processing earthquake in a frequency division way, extracting seismic attributes of different frequency bands, and adopting known well data analysis to preferably select seismic attributes better corresponding to the reservoir and the sand body; and finely describing the sand body by comprehensively adopting the geological rules, sand body seismic response characteristics and frequency-division seismic attribute analysis. The small sand body space quantitative description method comprises the steps of drawing the boundary of a sand body and determining a favorable area of a reservoir by the above method, and quantitatively describing the spatial shape of the sand body through well logging constrained inversion. The boundary of a described small sand body is accurate and quick to describe, and the accuracy of reservoir predication can be improved.