Based on the basic structure of deceleration sled, the paper established an simplified finite element model by Ansys/Ls-Dyna software, which is verified by GB 13057-2014 passenger seat simulating impact test and GB 27887-2011 child seat simulating impact test. Then, how the sled mass and the layout of the steel bars influence the decelerating curves are being discussed through the FE calculation: when the layout of the steel bars and the initial velocity of the sled remain unchanged, the heavier the sled is, the longer the deceleration curve continued; when the sled mass and the initial velocity remain unchanged, the more centrally the steel bars are being placed, the larger the peak value of the deceleration curve is. What’s more, the finite element model in this paper can provide some guidance in the daily tests.