The invention provides a preparation method of a fat-fighting low-calorie full-nutrition meal replacement preparation. The fat-fighting low-calorie full-nutrition meal replacement preparation is prepared from L-carnitine and common nutraceutical bulk pharmaceutical chemicals such as maltodextrin, rice meal, corn meal, soyabean protein powder, lactalbumin powder, sunflower seed oil, mineral substance mixtures, and vitamin mixtures, wherein the ratio of the L-carnitine is 1-6 percent. The L-carnitine has the function of improving the glucolipid metabolism, and an extremely-low-calorie high-protein diet has the functions of promoting the fat hydrolysis, lightening the hunger sensation, improving the lean body mass proportion and the like. Clinical and trial studies indicate that the fat-fighting low-calorie full-nutrition meal replacement preparation is accurate in treatment effect, is capable of rapidly reducing the weight within a short time, reducing the blood pressure, and improving the blood sugar, blood fat insulin sensitivity and liver functions, has a good prevention function on high blood pressure, diabetes and coronary heart disease, is capable of reducing adverse reaction in the dieting process and improving the tolerance of a human body to hunger, and has a good application prospect.