Aegilops tauschii is a competitive invasive weed typically found in winter wheat fields. In this study, using the replacement series experiments designed by de Wit, the effects of different shading treatments on the morphological structure, physiological characteristics, and competitiveness of the invasive plant A. tauschii were comparatively analyzed with the aim of providing knowledge for the ecological control of this weed in wheat fields. The results showed that in terms of morphological characteristics, shading caused an increase in plant height, leaf area, and specific leaf area (SLA); and a decrease in the root-to-crown ratio (R/C) of both A. tauschii and wheat plants. With regard to physiological characteristics, both A. tauschii and wheat plants adapted to the low-light environment by increasing the chlorophyll content, with an increase of chlorophyll b in particular. It could be concluded from the changes in superoxide dismutase (SOD) activity and thiobarbituric acid reactive substances (TBARS) content that the low-intensity shading treatment significantly improved the stress resistance of A. tauschii , thus ensuring the continuation of its normal photosynthesis. In addition, the plasticity index average value of eight morphological indicators of A. tauschii (e.g., plant height and leaf area) was 0.18, which was greater than that of wheat (0.17). Similarly, the plasticity index average value of four physiological indicators of A. tauschii (e.g., chlorophyll content and SOD activity) was 0.46, which was also higher than that of wheat (0.37). Finally, the competitive balance (CB) value of A. tauschii showed that its competitiveness under low light conditions was still greater than wheat, but gradually diminished with increasing shading rate. In short, A. tauschii displays a certain adaptability to low light environments, but shading treatment may also significantly reduce its competitive inhibition of wheat.