A pharmaceutical composition for preventing and treating senile dementia and a preparation method therefor. The active ingredients of the pharmaceutical composition are prepared from the following raw materials in weight part: 20 to 50 parts of epimedium and 15 to 55 parts of tuckahoe; or 20 to 50 parts of epimedium, 15 to 55 parts of tuckahoe and 10 to 55 parts of acanthopanax; or 20 to 50 parts of epimedium, 15 to 50 parts of tuckahoe, 15 to 50 parts of acanthopanax, and 6 to 15 parts of rhizoma anemarrhenae.