Fermentable sugars are a group of pivotal intermediates and platform compounds achieved by the conversion of lignocellulose. Fast pyrolysis, as a little-explored way to liberate levoglucosan from biomass, may have a potential capability to overcome the technical barriers and fundamental limitations for efficient saccharification. Pretreatment prior to fast pyrolysis is essential to improve levoglucosan yield from lignocellulose. Contrary to typical high-temperature acid pretreatments, a pretreatment under mild conditions was evaluated and optimized, where different acid (formic acid, acetic acid, oxalic acid, nitric acid, phosphoric acid, sulphuric acid and hydrochloric acid) were employed at room temperature prior to fast pyrolysis of lignocellulose. Due to the alteration of chemical compositions and physical structures of biomass, especially the elimination of alkali and alkaline earth metals, the levoglucosan yield of dilute acid pretreated biomass was improved remarkably as compared with that of raw material, meanwhile claimed that acid pretreatments at room temperature had an enough capability in efficient utilization of biomass. In sum, this study offered a novel and economical strategy for selective saccharification of lignocellulose for industrialized bio-refinery.