The invention discloses dietary fiber composite powder which is made of psyllium seed husk powder, chia seed powder, whey protein powder, whole milk powder, bovine colostrum powder, casein, moringa oleifera powder, oat powder or oat meal, oligosaccharide, polydextrose, sugar alcohol, collagen peptide powder, inulin, medium chain triglyceride, powdered oil, konjaku flour, carrageenan, rose powder,vitamin A, vitamin D, vitamin C, vitamin B1, vitamin B2, vitamin B6, vitamin B12, nicotinic acid, folic acid, pantothenic acid, iron, calcium, zinc, magnesium, taurine and L-carnitine in an appropriate ratio. The invention further provides a preparation method of the dietary fiber composite powder. After being eaten, the dietary fiber composite powder disclosed by the invention can be swelled withwater, then a person has the feeling of fullness after eating, the nutrition and the functionality of a dietary fiber composite powder product can be effectively improved, calorie intake can be reduced, intestinal environments can be improved, intestine and stomach functions can be improved, and diseases such as constipation and intestinal polyposis can be effectively prevented and treated.