The warps (curvatures) of strip in the continuous annealing can be classed as longitudinal and transverse warps. The analysis of warp is simplified from a three-dimensional elasticity problem to a plane problem, and it is proposed in this paper that the residual strain caused by metal rolling is the main reason for the transverse warps. The relationship between the different warps is also discussed on the basis of elastic analyses. Analytical estimates are derived and compared against field measurement. The warp mechanism on the strip steel production process is revealed which can provide the theory basis for decreasing warp.