The effects of annealing time on microstructure and mechanical properties of low silicon TRIP steel containing phosphorus and vanadium for hot-dip galvanization under ultra rapid heating were investigated. The results show that a high density of dislocations and the vanadium precipitate existe within matrix during ultra rapid continuous annealing, and most of the precipitated particle sizes are in the range from 4 to 10 nm. The volume fraction of retained austenite is increased with increasing annealed time, but the retained austenitic morphology is changed. The interlath retained austenite films with a thickness of 80－120 nm are　dominated with increasing annealed time to 90 s; the thickness of interlath　retained austenite films is increased to 200－600 nm and tended to block　structure continuing to increase the annealed time to 180 s. The yield and　tensile strength are decreased with increasing annealed time during ultra　rapid continuous annealing, however, the elongation and work harding index　are increased; the product of strength and ductility (R_m·δ) is decreased from   23976 MPa·% when annealed time is 10 s to 23625 MPa·% when annealed time is 180 s.