The subject of this thesis falls into the scope of Second Language Acquisition (SLA). In the past twenty years, SLA has developed into an independent and autonomous discipline, complete with its own agenda. And, it is also an interdisciplinary discipline, which involves the factors concerning linguistics, statistics, sociology, psychology and methodology etc. The subject of this thesis is focused on the classroom learning, which is an important part of SLA. The research largely finds its aid from analyses and experiments relating to the students learning activity in classroom.The thesis can be divided into four parts. Part one consists of two sections, in which the aim, methods, some terms and the theories concerning SLA research are particularly introduced. Section three presents some error data. According to theapproach of error analysis, these error data are examined in three levels-themorphological syntactical and pragmatic. Based on the results of analyses, a teacher can realize the habitual errors that a student tends to make. Section four and Section five are the third part, in which the discussion is focused on the issue of understanding, such as identification, interpretation and contextual accessibility. It is intended to make a microscopical study on the process of understanding what happens in the classroom. The primary aim is to make a teacher perceive the details of understanding procedure and know how to manipulate his teaching practice. Section six is the fourth part, which can be considered as a complement of the research. It is aimed at making a perspective on the English learning aided with multi-media from the view of linguistics. It presents a possible potential that the English learning aided with multi-media contains.