A method for calculating a tolerated dose of a human body to sugar alcohol and functional sugar selected from xylitol, L-arabinose and sorbitol, comprising the following steps: at step 1, selecting 200 g rats as experimental animal objects, and dividing the 200 g rats into six experimental groups and one control group, with each including ten numbered rats; gavaging different doses of xylitol, L-arabinose or sorbitol to the rats in the six experimental groups each day, wherein the ten rats in each group are gavaged with the same dose, and gavaging the same dose of sucrose or normal saline to the ten rats in the control group each day; providing enough drinking water and common feed to all the experimental rats each day, checking whether there is fecal matter at the anus of each rat in each group every night, wherein the existence of the fecal matter indicates that the rat has diarrhea, and making statistics on the quantity and numbers of rats with diarrhea; at step 2, continuing the step 1 for 14 days; at step 3, by combining the diarrhea situations of rats on the last day (day 14) with results of intestinal segment slice maps and diamine oxidase contents of the rats in each group, using a maximum dose group in which all the rats do not have diarrhea to obtain a maximum tolerated dose N of the rats in the group to xylitol, L-arabinose or sorbitol; at step 4, converting the maximum tolerated dose N of the 200 g rats to xylitol, L-arabinose or sorbitol according to the following conversion formula of drug doses of experimental animal and human body to obtain a tolerated dose R of the human body to xylitol, L-arabinose or sorbitol: 70 kg − human − body dose R = maximum tolerated dose N of 200 g rat × K wherein K is a conversion factor between a 70 kg human body and a 200 g rat, which is 56.0; the maximum tolerated dose N of the rat to xylitol, L-arabinose or sorbitol and the tolerated dose R of the human body to the xylitol, L-arabinose or sorbitol are both in the unit of g/d. at step 1, selecting 200 g rats as experimental animal objects, and dividing the 200 g rats into six experimental groups and one control group, with each including ten numbered rats; gavaging different doses of xylitol, L-arabinose or sorbitol to the rats in the six experimental groups each day, wherein the ten rats in each group are gavaged with the same dose, and gavaging the same dose of sucrose or normal saline to the ten rats in the control group each day; providing enough drinking water and common feed to all the experimental rats each day, checking whether there is fecal matter at the anus of each rat in each group every night, wherein the existence of the fecal matter indicates that the rat has diarrhea, and making statistics on the quantity and numbers of rats with diarrhea; at step 2, continuing the step 1 for 14 days; at step 3, by combining the diarrhea situations of rats on the last day (day 14) with results of intestinal segment slice maps and diamine oxidase contents of the rats in each group, using a maximum dose group in which all the rats do not have diarrhea to obtain a maximum tolerated dose N of the rats in the group to xylitol, L-arabinose or sorbitol; at step 4, converting the maximum tolerated dose N of the 200 g rats to xylitol, L-arabinose or sorbitol according to the following conversion formula of drug doses of experimental animal and human body to obtain a tolerated dose R of the human body to xylitol, L-arabinose or sorbitol: 70 kg − human − body dose R = maximum tolerated dose N of 200 g rat × K wherein K is a conversion factor between a 70 kg human body and a 200 g rat, which is 56.0; the maximum tolerated dose N of the rat to xylitol, L-arabinose or sorbitol and the tolerated dose R of the human body to the xylitol, L-arabinose or sorbitol are both in the unit of g/d.