The invention discloses a Penicillium oxalicum WX-209 strain with high cellulase yield and an enzyme producing method. The Penicillium oxalicum WX-209 is screened from rotten walnut skins in Wenxian County Gansu province, and the preservation number is CCTCC NO:M2013325. The method for preparation of a crude enzyme liquid by fermentation includes slant culture, ultrasonic pretreatment of a substrate (wheat bran), fermentation, enzyme liquid acquiring and other steps. The ultrasonic treatment of the substrate under ultrasonic power of 700-900W for 40-55min effectively improves the cellulase activity (in terms of CMCase enzyme) of the strain, and the improvement effect is significant compared with a non-pretreated control group. The strain provided in the invention has very good application prospects in cellulose degradation.