In this study, the effects of liquid digestate pretreatment of wheat straw on its biogas production efficiency and anaerobic digestion were investigated using a laboratory-scale biochemical methane potential test. Scanning electron microscope, X-ray diffraction analysis and Fourier transform infrared spectroscopy were used to analyze the changes in main compositions and physico-chemical structure of wheat straw after different pretreatment durations (3 days, 5 days, and 7 days). The results evidenced that liquid digestate pretreatment can dissolve the lignocellulosic structure, which positively promoted anaerobic biogas production. Liquid digestate pretreatment achieved a satisfactory anaerobic digestion efficiency with wheat straw as the substrate. Furthermore, the production of biogas and methane were also found to increase after pretreatment. Thus, it was concluded that a duration of 5-day liquid digestate pretreatment was optimal as it yielded 39.76% more biogas production, and 49.58% more biomethane yield, in 35.71% shorter digestion time (T-80) as compared to raw wheat straw. The modified Gompertz model was able to explain the kinetic behavior during anaerobic digestion of wheat straw. Based on the aforementioned experimental observations, a comparison between effects of equivalent NH4+-N concentration of ammonia solution and liquid digestate pretreatment was conducted, which indicated that ammonolysis played crucial role in the enhancement of biogas production process by pretreated liquid digestate.