Objective: To explore the pathogenesis of Eustachian tube dysfunction (ETD) in patients with chronic otitis media with effusion (COME) using middle ear pressure-equilibration testing. Methods: Pressure equilibration testing of ET ventilation function was carried out in 72 ears which included 51 ears of COME patients with ventilation tube (COME group) and 21 ears of patients with traumatic tympanic perforation (TP group). According to the results of the test, these ears were further divided into four types: 1. with both passive and active opening, 2. only with passive opening, 3. only with active opening, 4. without passive and active opening. Results: 85.7% ears in the TP group had both active and passive ET function while 88.2% ears in the COME group had ETD. The average frequency of ET opening (P<0.001) and the occurrence rate of pressure rebound wave (P<0.001) was significantly lower in the COME group, while the mean residual pressure after several swallowing acts (P<0.001) and the average ET opening duration (P=0.004) was significantly higher in the COME group than in the TP group. Conclusions: Relatively higher residual pressure, lower effective opening frequency, disappearance of rebound wave and longer ET opening duration indicate poor ET ventilation function and an abnormal contraction pattern of peritubular muscles of the ET in patients with COME. Our results show that ETD is prevalent in most patients with COME with various causes. Therefore, appropriate treatment methods should be adopted to ensure prompt and adequate recovery. Keywords: Eustachian tube function,pressure-equilibration test,chronic otitis media with effusion