The invention discloses a method for recycling phosphorus from sewage through bioelectrochemical struvite crystallization. The method aims to solve the problems that in existing recycling of phosphorus from sewage through bioelectrochemical struvite crystallization, an anode liquid is acidized, the overpotential is large, the magnesium source cost is high, and the like. Cheap magnesium ores are subjected to acidolysis in the anode liquid, acidification of the anode liquid is prevented, the overpotential is remarkably reduced, and the magnesium source cost is lowered. According to the method, based on a bichamber microbial electrolysis pool, under an extremely low externally applied voltage (0.3-1.2 V), an electrode reaction is performed to form conditions for acidification of the anode liquid and acidification of a cathode liquid; the crushed magnesium ores are added to an anode chamber, acidification of the anode liquid is prevented, the pH of the anode liquid is stabilized, and microorganisms are promoted to continuously degrade organic matter to generate power; and magnesium ions released through acidolysis of the magnesian cores move to an cathode through a cation exchange membrane under the drive of the electric filed force and has a crystallization reaction with ammonium radials and phosphate radicals under an alkaline condition, struvite deposits are formed, the pH of the cathode liquid is stabilized, and the purposes of removing and recycling the phosphorus from sewage are realized.