Focusing on the problems of tearing and folding，when mulching straw fiber film for tobacco through using plastic-film mulching machines on ridge，a tobacco mulching device on the ridge with wheat straw fiber film cultivation was designed. The mulching straw fiber film process was analyzed to establish the mathematical model of mulching straw fiber film on the ridge with correction coefficient and the main factors affecting tearing of straw fiber film was proposed，when mulching straw fiber film. The structural parameter range of the key components was analyzed and confirmed and the structural parameter ranges were got, aiming at the guide roller of side of film and the device pressing side of film and mulching and pressing soil on the side of film etc.Three factors three levels orthogonal test was used，the distance between the roller of flattening film and the roller pressing side of film，the inclination angle of the guide roller of side of film and working speed were selected as test factors.The outspread degree and rate split by film-covering drill of light-struck film were taken as evaluation indexes.The results showed that the working speed and the distance between the roller of flattening film and the roller pressing side of film had an significant effect on rate split by film-covering drill of light-struck film (0.01＜P＜0.05). The effect of the inclination angle of the guide roller of side of film on the outspread degree was extremely significant (P＜0.01)．The results of verification test were as follows：the working speed was 3.6km/s, the distance between the roller of flattening film and the roller pressing side of film came to be 120cm, the inclination angle of guide roller of side of film reached 30°，such outspread degree was 97.4%，and rate split by film-covering drill of light-struck film was 12.6mm/m2. The device mulching wheat straw fiber film can achieve agricultural need and mechanization of film mulching machine on the ridge for tobacco cultivation.