The Moho interface provides critical evidence for crustal thickness and the mode of oceanic crust accretion.The seismic Moho interface has not been identified yet at the magma-rich segments(46°–52°E)of the ultraslow spreading Southwestern Indian Ridge(SWIR).This paper firstly deduces the characteristics and domains of seismic phases based on a theoretical oceanic crust model.Then,topographic correction is carried out for the OBS record sections along Profile Y3Y4 using the latest OBS data acquired from the detailed 3D seismic survey at the SWIR in 2010.Seismic phases are identified and analyzed,especially for the reflected and refracted seismic phases from the Moho.A 2D crustal model is finally established using the ray tracing and travel-time simulation method.The presence of reflected seismic phases at Segment 28 shows that the crustal rocks have been separated from the mantle by cooling and the Moho interface has already formed at zero age.The 2D seismic velocity structure across the axis of Segment 28 indicates that detachment faults play a key role during the processes of asymmetric oceanic crust accretion. The Moho interface provides critical evidence for crustal thickness and the mode of oceanic crust accretion. The seismic Moho interface has not been identified yet at the magma-rich segments (46 ° -52 ° E) of the ultraslow spreading Southwestern Indian Ridge (SWIR) . This paper created deduction of characteristics and domains of seismic phases based on a theoretical oceanic crust model. Chen, topographic correction is carried out for the OBS record sections along Profile Y3Y4 using the latest OBS data acquired from the detailed 3D seismic survey at the SWIR in 2010. Seismic phases are identified and analyzed, especially for the reflected and refracted seismic phases from the Moho. A 2D crustal model is finally established using the ray tracing and travel-time simulation method. The presence of reflected seismic phases at Segment 28 shows that the crustal rocks have been separated from the mantle by cooling and the Moho interface has already formed at zero age.The 2D seismic velocity structure acros s the axis of Segment 28 indicates that detachment faults play a key role during the processes of asymmetric oceanic crust accretion.