The work aims to improve adhesion between film and substrate by studying the effects of plasma etching pretreatment on and the substrate. Anode-layer ion source was used to treat the M50 steel sample provided with different ion source power and treatment time, and tungsten doped DLC film was prepared on surface of the treated sample. Surface morphology of the sample before and after plasma etching treatment was studied by virtue of an atomic force microscope; microstructure of the film was analyzed by using a Raman spectroscopy; adhesion between film and substrate was studied by using a scratch tester. Different ion source power and plasma etching time led to different substrate micro surface roughness; with D peak and G peak values close to 1350 cm?1 and 1580 cm?1, Tungsten doped DLC film was typical diamond like carbon structure, its ID/IG value was nearly 1.5; adhesion between film and substrate not subject to plasma etching pretreatment was 23 N while that of the sample subject to plasma etching pretreatment was up to 69 N; the best ion source power and etching time were 2 kW and 60 min respectively. Plasma etching pretreatment can improve the adhesion between the film and substrate effectively.