Abstract: Objective To analyze the features of surface electromyography(sEMG) signal of the thigh muscle in convalescent stroke patients during knee voluntary extension and flexion. Methods Thirty-five stroke patients with who suffers spastic hemiplegia in Taizhou Hospital of Zhejiang Province from July,2013 to December,2014 and age-and sex-matched normal controls were involved in this study.The signals of sEMG of root mean square value(RMS) and co-contraction ratio(CR) from the patients and controls were compared. Results The knee extension in patients with bilateral quadriceps,biceps femoris RMS value were significantly decreased compared with normal control group(P<0.01),and health,ipsilateral RMS values significantly different(P<0.01);when knee,ipsilateral quadriceps and biceps femoris of RMS values are less than the normal control group,there was a significant difference(P<0.01),and health,ipsilateral RMS values significantly different(P<0.01);patients with contralateral medial femoral biceps muscle and the RMS value of the shares is less than the normal control group,but there was no significant difference(P>0.05);When knees,ipsilateral and contralateral CR greater than the normal control group,there was a significant difference(P<0.05);contralateral CR was less than normal control group showed no significant difference(P>0.05);knee extension,ipsilateral and contralateral CR were greater than the normal control group,there was a significant difference(P<0.05). Conclusion There are initiative antagonistic muscle coordination abnormal in the hemiplegic patients after stroke spastic muscle flexion ipsilateral healthy muscle.The SEMG technology in real-time quantitative evaluation of stroke patients after knee spastic muscle control disorders and active antagonistic muscle coordination,and provide a strong basis prognosis for the development and evaluation of rehabilitation programs.