Muscle fatigue is one of the main reasons for cervical spondylosis. In order to effectively detect and relieve cervical muscle fatigue, the relation between surface electromyography (SEMG) and cervical muscle fatigue was investigated based on biomechanics. In the experiments, 8 healthy volunteers aged between 21 and 33 years old were selected as subjects. All the subjects maintained cervical flexion positions for 2 hours, and the SEMG signals of upper trapezius at 6th and 7th spinous processes were recorded. First, empirical mode decomposition (EMD) was used to denoise the SEMG signals. Then, integrated electromyography (IEMG), approximate entropy (ApEn), and fatigue index Q were extracted and analyzed; the changing rules of the three characteristic parameters in cervical flexion process were studied. The experiment results show that as the neck flexion time increases, the IEMG increases, ApEn and index Q decrease. Among the three parameters, index Q has the best relation with muscle fatigue due to the stable data, obvious difference and being consistent with biomechanical analysis. During the 2 hours of cervical flexion, the average value of index Q decreases from 0.37 to 0.21. Then, it increases to 0.33 after massage. Therefore, the research results have great significance for the people suffering from long time cervical flexion to avoid and relieve cervical muscle fatigue and reduce the occurrence of cervical spondylosis.