Combined pretreatment using CaO and the liquid fraction of digestate (LFD) was proposed as an eco-friendly pretreatment method for high-quality anaerobic digestion (AD). In this study, rice straw was pretreated by CaO-LFD at three pretreatment temperatures (5, 20, and 35 degrees C) and four pretreatment times (1, 2, 3, and 4 days). The results showed that the optimum pretreatment condition for rice straw was 35 degrees C for 2 days. In this case, the maximum biomethane yield reached 308 mL g(-1) of VS, 77.4% higher than that of the control. The Fitzhugh and Cone models were demonstrated to be more suitable for CaO-LFD pretreated rice straw in the AD process. AD of pretreated rice straw had a shorter effective biomethane production period and lag phase time, exhibiting high AD efficiency. This study enhances the knowledge about CaO-LFD pretreatment from multiple angles, in addition to demonstrating promising possibilities for practical application.