Solid acid catalyst has high catalytic esterification activity but with a free acid excess problem. In this paper, washing pretreatments were adopted in the catalyst preparation processes and their influences on catalytic activity and residual free acid amount were investigated. Residual free acid amount can be reduced by 33% with both washing before calcinations and washing after calcinations pretreatments. But their influences on catalyst activities were different. Washing before calcinations pretreatment reduced the catalytic activity from 80.29% to 57.72% while the other washing pretreatment had little influence on the catalyst activity. In order to describe the influence mechanism of washing pretreatments, catalysts were characterized by FT-IR and XRD. Finally, typical compounds in bio-oil were selected to form a bio-oil model compounds system. The catalyst pretreated by washing after calcinations was used on the esterification research of this bio-oil model system. The volume ratio of propanol to bio-oil model compound was 3:1. The reaction temperature was 90 °C and the amount of catalyst was 2wt% of total liquid mass. Combined with the GC-MS qualitative and quantitative results, carboxylic acids, such as formic acid, acetic acid, propionic acid were converted to esters effectively.