After coinoculation of rumen fluid with sludge, the methanogenic efficiency and anaerobic fermentation characteristics of straw which were influenced by combination of different digestate recirculation ratios and organic loading rates (OLR) at six stages, were studied in a semicontinuous reactor with solidfeeding device. The results showed that methane yield reached 768mL/(L·d) at4g/(L·d) of OLR and 1∶1 of digestate recirculation ratio. Methane production was 202mL/g (217mL/g) at this stage, which had obvious cost advantage. However, VFAs were accumulated significantly with propionate concentration being as high as 6.54g/L while ammonia nitrogen concentration reached 63251mg/L at 6g/(L·d) of OLR. Degradation degree of cellulose and hemicellulose in solid residues reached 88.81% at phase 2 whereas hydrolytic activities correlated with methanogenic efficiency. Through the analysis of three dimensional fluorescence spectrum, it was found that dissolved organic matters of tyrosinelike component, coenzyme F420 and humic acid were affected by digestate recirculation ratio and OLR. The changes of the components could directly reflect the methaneproducing activities and fermentation characteristics. Moreover, accumulation of humic acid was responsible for decrease of methanogenic activity. Therefore, proper digestate recirculation ratio and OLR were indispensable to longterm stable operation of biogas engineering from straw by avoiding the accumulation of harmful components in liquid digestate.