In order to study the effect of seed coating agent on photosynthetic characteristics of cotton seedlings under low temperature, we used “Xinluzao 57” as material with pot culture method, the temperature is set to 10, 18 ℃ and the stress time are set to 0, 1, 2, 3 day, from three aspects of photosynthetic pigments, photosynthetic gas exchange parameters and chlorophyll fluorescence kinetics to investigate the relieving effect of seed coating agent on low temperature damage of cotton seedlings. The results show: (1) compared with the uncoated cotton seedlings, seed coating can improve the cotton seedling chlorophyll a, b and carotenoid contents under low temperature stress, but at normal temperature, seed coating agent had no significant effect on the photosynthetic pigment contents of the cotton seedlings. (2) Compared with uncoated cotton seedlings, after 10 ℃ and 18 ℃ low temperature treatment for 3 d, coated cotton seedlings net photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance (G_s) increased 33.71%, 52.00%, 96.63% and 38.57%, 55.17% and 103.42%, respectively, intercellular carbon dioxide concentration (C_i) reduced by 15.15% and 11.12%, respectively. (3) Compared with uncoated cotton seedlings, after 10 ℃ and 18 ℃ low temperature treatment for 3d, the absorption of light energy in the unit reaction center (ABS/RC) of the coated cotton seedlings increased 0.41% and 1.56%, respectively. The energy used to restore the Q_A (TR_o/RC) and the capture of energy for electron transfer (ET_o/RC) increased 2.97%, 0.47% and 4.27% and 1.67%, respectively. The reaction center for exciton electron transfer and to promote the reduction of Q_A exciton ratio (ψ_o) increased 0.18% and 2.16%, respectively. The absorption of light energy for the quantum yield (Φ_Eo) and the performance index (PI_ABS) of electron transfer increased 2.25%, 2.42% and 19.32% and 5.94%, respectively. The results, indicated that coating agent treatment can improve the content of photosynthetic pigments in cotton seedlings, regulate stomatal opening, enhance the fixation and utilization of CO₂, increase the energy of photosynthetic absorption and capture, and induce reasonable distribution of photosynthetic energy, maintain the absorption, capture and transformation of light energy in the photosynthetic organs, thus mitigate the damage caused by low temperature stress.