The purpose of this paper is to improve the English teaching levels of colleges and universities. First, the primary attributes of dynamic nonlinear system theory in second language acquisition are analyzed. Second, the influencing factors of English grammar application ability in theoretical dimension and measurement methods are proposed. Six first-year students majoring in English in a university were randomly selected as research objects, who were followed up for a semester, during which three identical oral English tasks were finished (in September, October, and November of 2020). The fluency, accuracy, and complexity of students’ utterances are statistically analyzed using SPSS 26.0. Results demonstrate that the fluency of students’ utterances has increased from 110 syllables per minute on average in September to 129 syllables per minute on average in November. The proportion of error-free clauses has increased from 0.5 to 0.55, and the number of clauses in the T unit has increased from 1.42 to 1.51. Students [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] have a gradually increasing accuracy of utterance, while student [Formula: see text] shows a gradually decreasing utterance accuracy. Students [Formula: see text] and [Formula: see text] have a decreasing utterance accuracy, while students [Formula: see text] and [Formula: see text] present an increasing utterance accuracy. Besides, the utterance accuracy of students [Formula: see text] and [Formula: see text] first decreases and then increases. The performances in utterance complexity of students [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] have been increasing gradually, while the performance of student [Formula: see text] has been decreasing gradually. The normal distribution of each student’s test scores is different, as well. Hence, any minor changes will affect the overall oral English levels of students.