The invention discloses nutritional meal replacement powder with the effect of reducing weight and fat, and a preparation method thereof. The preparation method comprises the following steps of: preparing gelatin and CMC (carboxy methylated cellulose) into enveloped capsaicine by utilizing complex coacervation method, and uniformly and sufficiently mixing the enveloped capsaicine with L-carnitine, resistant starch, konjac flour, soybean peptide and hericium erinaceus polysaccharide in a weight ratio. According to the meal replacement powder, the enveloped capsaicine and the L-carnitine are compounded, the effect of metabolizing fat of the L-carnitine is reinforced by utilizing the characteristics of promoting fat metabolism and controlling appetite of the enveloped capsaicine, the weight reducing function of the L-carnitine can be given a full play, and weight can be reduced more effectively. Furthermore, the body nutrition intake can be strengthened, and digestive health can be protected, the meal replacement powder is compounded of a plurality of food components which can be used for reducing food intake, promoting body fat metabolism and excretion, and replenishing nutrients required by the body and has a good taste. The meal replacement powder has an excellent effect on obesity, overweight and body shaping. Compared with a product with single weight reducing effect or Western medicines with side effects, the meal replacement powder has remarkable advantages, is a novel weight reducing product, and has an bright market application prospect.