Large quantities of burned or abandoned rose stalks are leading to serious environmental pollution. In this study, the effect of the moisture content of a solid-state NaOH pretreatment on methane production was first determined by a biochemical methane potential test. Then, the effect of codigestion with pig manure on methane production was investigated under the optimal moisture via thermophilic semi-dry anaerobic digestion by leaching bed reactor. Biogas production kinetic was assessed by the first-order kinetic model and modified Gompertz model. An increase in methane yield and biogas production kinetics was shown in the solid-state NaOH pretreated biomass. There was no significant difference in methane production for the three moisture contents studied during pretreatment (54%, 70%, and 77%). The anaerobic codigestion of rose stalk and pig manure increased 41% to 52% for methane yields and improved biogas production kinetics compared with monodigestion of rose stalk. Anaerobic codigestion did not greatly change the process stability, except for NH4+-N. The optimal process for the anaerobic digestion of rose stalk was as follows. The rose stalk was initially pretreated via solid-state NaOH pretreatment with a moisture content of 70%. Then, the pretreated rose stalk was co-digested with pig manure at a total solids ratio of 1:1.