Light olefins are the key and basic feedstock of the organic chemical industry. In this study, the effects of Ce-, Mg-, Fe-, and P-modified HZSM-5 on the formation of light olefins from the ex situ catalytic fast pyrolysis of wheat straw were explored in a fixed-bed reactor. Catalysts containing 1, 3, and 5 wt % modifiers were prepared by the equal volume impregnation method and characterized by surface area and porosity analyzer, X-ray diffractometer, and NH3 temperature-programmed desorption analytical instruments. The promotion effect on the yield of light olefins of modified HZSM-5 follows the decreasing order of Ce, Mg, P, and Fe. Moreover, with the increase in loading amount, the yield of light olefins was increased sharply by Ce/ZSM-S, and it was increased slightly or negligibly by P/ZSM-5 or Mg/ZSM-5, whereas it was decreased by Fe/ZSM-S. Overall, the highest yield of light olefins was achieved for 9.18 C-mol % at 5 wt % Ce loading, which could be due to its high total acid amount and smaller average pore size.