Abstract: 【Objective】Discussed the chlorophyll fluorescence physiological mechanism of summer maize yield deduction caused by drought stress at silking stage and provided theoretical basis for drought resistant cultivation of summer maize.【Method】The summer maize cultivars of Zhangdan 958 and Xianyu 335 were used as test materials. The experiment with two water treatments of sufficient irrigationCK, the soil moisture content was(75±5)% of the maximum field water capacity in 0-20 cm soil layer and drought stress the soil moisture content was(45±5)% of the maximum field water capacity in 0-20 cm soil layer were applied in drought pool with rain shelter. Determined the SPAD value and chlorophyll fluorescence parameters of ear leaf at silking stage(0 d) and after silking stage, and investigated the spike characters and yield of summer maize.【Result】Drought stress significantly influenced the SPAD value and chlorophyll fluorescence characteristics. Drought stress declined leaf SPAD value at silking stage and after silking stage, and the biggest decline of Zhengdan 958 and Xianyu 335 with 15.38% and 17.65% respectively occurred at 20 d after silking. Under drought stress, photosystemⅡ(PSⅡ) maximum photochemical efficiency(F_v/F_m) and potential activity(F_v/F_o) of ear leaves of the two summer maize varieties declined significantly(P<0.05, the same below), and the decline was strengthened as drought stress time extended. The decline at 20 d after silking was the largest, which were 0.036 and 0.574 respectively for Zhengdan 958, 0.039 and 0.593 respectively for Xianyu 335. Simultaneously, drought stress decreased index of photosynthetic performance(PI_ABS) of ear leaf, the influence was enhanced as drought stress time extended. The most decline were achieved at 20 d after silking with 12.30% and 16.87% respectively for Zhengdan 958 and Xianyu 335. Additionally, when water supply was restored after drought stress, leaf chlorophyll content and chlorophyll fluorescence parameters(F_v/F_m, F_v/F₀ and PI_ABS) at 40 d after silking under drought stress were lower than CK, but the difference between the two treatments was dwindled. Drought stress extended bald ear length, decreased kernels per spike and thousand-kernel weight significantly, resulted in reduction of yield by 10.29% and 11.83% respectively for summer cultivar of Zhengdan 958 and Xianyu 335.【Conclusion】Drought stress at silking stage causes the irreversible damage to chlorophyll in ear leaves, which decreases SPAD value, F_v/F_m, F_v/F₀ and PI_ABS, restricts leaf photosynthesis, and results in reduction of output for summer maize.