This paper studied the effects of short- and long term abscisic acid (ABA) treatments on the CO2 assimilation (Pn), carboxylation efficiency (CE), response of Pn to CO2, and antioxidant enzyme activities of wheat seedlings exposed to UV-C. The results showed that under no UV-C, short- and long term ABA treatments increased Pn by 14.69% and 20.46%, and decreased stomatal conductance (Gs) by 14.74% and 17.31%, respectively, compared to the control, while no effects were observed on intercellular CO2 concentration (Ci) and CE. Under UV-C, the Pn, CE, Gs and Ci decreased, with the least decrease in long term ABA treatment, less in short term ABA treatment, and the most in control. ABA could increase the response of Pn to CO2, while UV-C inhibited it. In ABA treatments, antioxidant enzyme activities were enhanced, while MDA content was decreased. Under UV-C, CAT activity increased first, reached its maximum after 1 h, and decreased then. The activities of SOD and POD in ABA treatments increased first and decreased then, with the greater increase in long term ABA treatment than in short term ABA treatment, while those in the control decreased. It was suggested that through enhancing Pn and antioxidant enzyme activities, ABA could enhance the resistance of wheat to UV-C, and long term ABA treatment had better effects than short term ABA treatment.