Abstract: Taking the cold-rolled annealed high strength steel HC440/780DHD+Z as the research subject, the tensile deformation of the samples with different pre-strains was carried out by uniaxial tensile testing machine. The mechanical properties, microstructure and residual austenite content of the speec after pre-tension were analyzed and evaluated. The results show that the microstructure of DH780 steel is composed of ferrite, martensite and a small amount of residual austenite,of which the volume fraction of residual austenite is about 4.2%. Compared with those of DP780 steel, due to the TRIP effect of residual austenite,DH780 steel has higher elongation,work hardening index and cupping values, but the hole expansion rate is lower. With the increase of pre-strain, the metastable residual austenite gradually transforms to martensite, and the residual austenite content gradually decreases until it tends to be stable. The yield strength and tensile strength increase correspondingly, and the yield strength ratio increases from 0.564 to 0.959. At the same time, the work hardening index decreases gradually, and the elongation changes little.