The invention discloses a method for preparing a vehicle
urea solution. The method comprises the following steps: treating industrial desalted water by a
reverse osmosis device, a microporous filter and an EDI electric deionizing device and then sterilizing to obtain high purity water, wherein the resistivity of the high purity water is equal to or greater than 16 Momega.cm at 25 DEG C; mixing the high purity water with a high temperature
urea solution which is subjected to
ammonia and CO2 removal by virtue of
flash evaporation during production of
urea to prepare a urea
aqueous solution with the concentration of 48-55wt% and the temperature of 68-72 DEG C; then cooling to 18-25 DEG C, filtering to obtain crystallized urea, mixing the crystallized urea and the high purity water to prepare another urea
aqueous solution with the concentration of 31.8-33.2wt%; finally filtering by a filter film with the aperture of 0.2-0.5 micron to obtain the final vehicle urea solution. According to the method, the vehicle urea solution is directly produced without an external heating source, the contents of biuret,
metal ions, insoluble substances and the like are relatively low, the method is especially suitable for directly producing vehicle urea in a urea production factory, and the cost during production is reduced.