The invention discloses a preparation system of car urea. The preparation system comprises a raw water tank (1), a raw water pump (2), a gravel filter system (3), an active carbon filter system (4), an ion exchange softening device (5), a pressurizing pump (6), a micro filter device (7), an ultra-filtration device (8), a middle water tank (9), a high pressure pump (10), a primary reverse osmosis device (11), a secondary reverse osmosis device (12), an EDI (electronic data interchange) system (13), an urea water barrel (14), a material storage tank (15), a primary filter system (16), a homogenization system (17), a discoloring system (18), a purifying system (19) and a filling device (20) which are connected in sequence by a pipeline. The system is reasonable in structural design, wide in range of application, good in equipment mating performance, high in automation degree, high in operability, small in floor area, capable of removing various ions in water, capable of reaching a salt removing rate of over 99.5%, stable in operation and high in utilization rate.