The invention relates to a method for synthesis of 
calcium alginic acid monosaccharide from shells and 
alginic acid. The method comprises shell pre-treatment, 
alginic acid degradation, synthesis, 
crystallization, and 
drying. The method comprises the following steps of 1, immersing shells in 
hydrochloric acid having the content of 0.05M, carrying out 
drying, carrying out crushing, carrying out treatment by an 
elutriation method to obtain 
calcium-source shell 
powder, adding alginic acid into an appropriate amount of a H2O2 solution having the content of 3%, carrying out heating degradation by a water-bath heating and 
microwave heating 
combined method, wherein in the heating degradation, a water-bath heating process is carried out at a temperature of 80 DEG C for 1h, then a 
microwave heating process is carried out for 1.5h, then a water-bath heating process is carried out at a temperature of 80 DEG C for 1h and then a 
microwave heating process is carried out for 1h, and carrying out 
centrifugation, purification, concentration and 
drying of the degradation products to obtain white alginic acid 
monosaccharide, and 2, dissolving the white alginic acid 
monosaccharide in an appropriate amount of 
distilled water, adding the 
calcium-source shell 
powder into the alginic acid monosaccharide solution according to a 
mole ratio of the alginic acid monosaccharide to the shell 
powder of 2: 1.0-1.2, wherein the 
calcium carbonate content is 95%, carrying out a reaction in a water bath at a temperature of 30 DEG C for 0.75h, carrying out suction 
filtration, and carrying out reduced pressure concentration, 
alcohol precipitation crystallization and drying of the supernatant. The method has simple processes. The calcium alginic acid monosaccharide can be used as a novel 
calcium supplement agent. The method realizes high-value utilization of alginic acid and a plurality of shells.