Abstract: In order to make effective utilization of wheat straw and reduce environment pollution from the burning of wheat straw, this paper investigated the pretreatment method with the dilute alkali for wheat straw as raw material in composites. The effects of the concentration of sodium hydroxide solution，liquid-solid ratio, processing temperature and time on the weight loss rate of wheat straw were studied. The mechanical properties, surface structures and contact angles of the treated wheat straws were tested. The results showed that the optimized processing parameters with dilute alkali were as follow: liquid-solid ratio was 30, concentration of sodium hydroxide solution was 4%， processing temperature was 100℃ and processing time was 60 min. The mechanical properties of wheat straw fibers prepared with above processing parameters had no significant changes. Compared with untreated wheat straw, the inner and outer surface structures of the treated wheat straws were looser, their specific surface area increased and contact angle decreased. The above structure changes would improve the infiltration property of polylactic acid to the wheat straw fibers and the interfacial bondability. The research can provide a reference for further research on new eco-friendly composites based on wheat straw fibers and polylactic acid.