The influence of MJO on El Nio events in the western tropical Pacific is explored from the perspective of Kelvin waves. A Kelvin waves index (K) by wind stress associated with MJO is derived from surface wind data. The index represents the intensity of Kelvin waves. By comparing the changes of the index K and the depth of main thermocline, it is denoted that when strong MJO-related Kelvin waves appear in the development of El Nio and the eastward waves convey anomalous downwelling signals of the thermocline, the SSTA amplitudes will be enhanced, which significantly promotes the development of El Nio, such as 1997/1998 El Nio; weak MJO-related Kelvin waves have little influence on El Nio events and such waves with anomalous upwelling signals will even hinder the occurrence and development of El Nio events. In general, MJO events in the western tropical Pacific have significant influence on El Nio events in some special cases, but they are not the key factors in the occurrence or termination of El Nio events.