The invention discloses a nontoxic mosquito-repellent incense liquid and a preparation method thereof. The nontoxic mosquito-repellent incense liquid is prepared from following raw materials, by weight, 18 to 24 parts of cassia twig extract, 4 to 9 parts of mangosteen peel extract, 12 to 17 parts of folium cycadis revolutae extract, 90 to 100 parts of deionized water, and 95 to 110 parts of ethanol. The preparation method comprises following steps: the cassia twig extract, the mangosteen peel extract, and the folium cycadis revolutae extract are prepared respectively via ultrasonic treatment, centrifugation, condensation, and drying; the cassia twig extract, the mangosteen peel extract, the folium cycadis revolutae extract, deionized water, and ethanol are mixed, and an obtained mixture is sealed, and is stirred for 5 to 6h at 40 to 45 DEG C so as to obtain the nontoxic mosquito-repellent incense liquid. The nontoxic mosquito-repellent incense liquid is nontoxic, is capable of sterilizing, driving mosquito away, and improving sleep; the raw materials are easily available; cost is low; the preparation method is simple, and is convenient for industrialized production.