The invention relates to the technical field of sewage treatment, in particular to a multistage filtering and extracting system. An extracting device is connected to a concentrated solution outlet end of a membrane filter and provided with a taking outlet and a waste liquid discharge port, a biochemical treater is connected to the other end of the waste liquid discharge port, and a discharge port of the biochemical treater is connected with a purifier. Sewage is filtered through a hollow fiber filtering membrane, concentrated solution obtained after filtering is extracted to obtain useful substances and waste liquid, the waste liquid is subjected to biochemical treatment and purification, and concentrated solution generated at each step is subjected to extraction by means of specific proper methods such as ion exchange or ionization crystallization to extract useful substances for recycling.