For the problems caused in the coldformed process at corners of high strength steel square tube, i.e. poor mechanical properties, severe hardening and residual stress concentration, a local induction tempering process online was proposed. This process could effectively solve the problems of corner defects of coldformed high strength steel square tube. The study found that the different tempering temperatures had a great impact on the mechanical properties of the bending angle. The results showed that the strength and elongation of the tempering square tube were almost the same as those of the vigor material at tempering temperature of 650℃. There was no crack when the displacement distance was larger than 1/2 of diagonal length at flattening test. The magnitude and distribution of the residual stresses had also been improved to some extent. As the tempering temperature was 700℃, the strength of the high strength steel square tube decreased, the heat affected zone became larger, and the distribution of the residual stresses got abnormal.