The invention provides a method for extracting and purifying 
sugar alcohol with high purity and high yield, which comprises the following steps of: performing partial purification on the 
sugar alcohol in a 
raw material solution through a 
microfiltration-
ultrafiltration-
nanofiltration process, and removing 
protein impurities in the 
raw material solution by using an 
ultrafiltration membrane to achieve the effects of improving the 
nanofiltration concentration multiple, reducing the 
chemical cleaning frequency and improving the purity of the 
sugar alcohol; guiding concentrated water of the first-section micro-
filtration membrane device and concentrated water of the first-section nano-
filtration membrane device into a second-section micro-
filtration membrane device and a second-section nano-
filtration membrane device respectively again to conduct circulating concentration on feed liquid, and guiding concentrated water of the second-section nano-
filtration membrane device into a third-section nano-
filtration membrane device to conduct concentration again; enabling the 
produced water of the 
reverse osmosis membrane device to flow back to the inlet water of the second-section micro-filtration membrane device and the third-section nano-filtration membrane device, so that the concentrated water of the first-section micro-filtration membrane device and the concentrated water of the second-section nano-filtration membrane device are diluted, and the 
produced water of the second-section micro-filtration membrane device is used for diluting the concentrated water of the first-section nano-filtration membrane device, and therefore, the 
transmittance of 
sugar alcohol in the concentration process is further increased, the concentration load of two-section 
nanofiltration and three-section nanofiltration is reduced, meanwhile, the 
resource consumption is greatly reduced, and a complete internal circulation is formed; the method provided by the invention provides an efficient non-batch switching operation process for the purification of 
sugar alcohol, and maximizes the stability and continuity of a process line under the condition of further improving the product yield and purity.