The invention relates to a forewarning method and a forewarning system of road vehicle curve side rollover. The forewarning method and the forewarning system of the road vehicle curve side rollover are characterized by comprising the steps: carrying out real-time detection on a vehicle which runs in a curve, obtaining vertical shearing stress of a vehicle shaft end portion and a wheel vertical accelerated speed corresponding to the vehicle shaft end portion, and thus obtaining contact force between wheels and the ground; obtaining a side rollover factor of each vehicle shaft according to the contact force, and then obtaining a comprehensive side rollover factor of all vehicle shafts in a weighting mode, and sending out a warning through an alarm device when the weighted comprehensive side rollover factor exceeds a side rollover factor critical value. The forewarning method and the forewarning system of the road vehicle curve side rollover can enable road vehicle curve travel to be safe and reliable, and effectively reduce possibility of occurrence of side rollover risks.