Abstract: On the basis of that use researches of using time-lag nature-oscillator equation to study the nonlinear evolution features of the sea temperature of the eastern equatorial pacific, and according observational data, the time-lag nature-oscillator equation for description of the evolution of the sea temperature was retrieved. According to the equation, the perturb theory and the stable theory of differential equation, some significant results about the eastern equation pacific sea temperature were obtained as follows. ①The calculated time-lag that is τ=14 month agrees with the period that is from several months to 2 years when the stimulated western Rossby wave arrived at the Pacific west coast and then was reflected to the researched region as Kelvin wave. ②Under the condition of the zero order approximation and the effects of the time-lag, the sea temperature evolution of the eastern equatorial Pacific has the stable El Nino phase and the stable La Nina phase. ③ Under the condition of the first order approximation, when the earlier stage sea temperature of the eastern equatorial Pacific is far away from its average value, the sea temperature system is a stable dynamic system, that is with the increasing of time t, the temperature tends to be near the average. Once the sea temperature has tended to be around its average, the sea temperature system of the eastern equatorial Pacific probably becomes an unstable dynamic system, that is the sea temperature of the eastern equatorial Pacific is far away from its average with the increasing of the t. So the principal evolution picture that the sea temperature of the eastern equatorial pacific oscillates from El Nino phase to La Nina phase, and vice versa, are obtained. ④According to τ=14 month, the result was also obtained that the sea temperature of the eastern equatorial Pacific has quasi-triennial oscillation periods, whether or not the sea temperature system of the eastern equatorial Pacific is stable.