According to the methodology by Intergovernmental Panel on Climate Change (IPCC), environmental and energetic impact of biogas production from the biomass composed of plant solidago canadensis L.(SC) and sewage sludge was evaluated in the study. Environmental evaluation focused on greenhouse gas (GHG) reduction, which was estimated from the methane yield through lab-scale anaerobic co-digestion of high-solid dewatered sludge (DS) and un-pretreated SC feedstocks with different volatile solid (VS) ratio of SC at mesophilic temperature. While energetic evaluation took into account the direct and indirect energy inputs of sludge storage and spreading, escaping of biogas from the digested effluent, and the addition of chemical fertilizers and reagents. These results indicated that anaerobic co-digestion of SC and DS to produce biogas was a high energy-efficient and environmentally friendly process. The net GHG emissions decreased with shortened SRT and increased portion of SC in the feedstock, and co-digestion of SC and DS at SRT of 20d with 50% VS addition of SC showed higher energy efficiency and significantly GHG reduction. Compared with the case with no SC, the addition of SC in the anaerobic digestion could achieve about 78 % reduction of net GHG emission. Besides, biogas plant operation was the largest energy consuming unit, in which stirring accounted for 39.5%~42.9% of the entire energy consumption of anaerobic digestion.