The invention discloses a preparation method of modified talcum powder. The preparation method includes the steps that by weight, 0.1-0.18 part of carboxymethyl chitosan, 0.4-0.6 part of vitamin C, 0.2-0.3 part of instant CMC and 100 parts of water are taken and prepared into a water solution at normal temperature, the water solution is rapidly heated to 70 DEG C, the temperature is kept for 30 s, and then the water solution is restored to normal temperature; 2, by weight, 5 parts of talcum powder and 50 parts of purified water are added, after the mixture is fully stirred to be mixed to be uniform, 0.05 part of the solution prepared in the step 1 continues to be fully stirred and mixed for 20 min at the speed of 600 r/min, 0.2 part of 2 wt% aluminum sulfate solution is added at a time, the mixture continues to be stirred for 5 min, and modified talcum powder suspension is washed and filtered; 3, the modified talcum powder is re-dispersed in water, microwave treatment is carried out for 2 min, and the modified talcum powder is obtained.