【Abstract】This paper mainly investigated the frequent errors found in English writings of Chinese non-English major students. Students’ argumentative writings on the topic of “computer” were collected and analyzed. The mostly frequent types of errors were classified and analyzed. Besides， the sources of errors were also discussed from two perspectives：interlingual source and intralingual source. The present paper also provided some pedagogical implications for English writing teaching.
　　【Key words】Errors； English writing； Interlingual； Intralingual
　　1. Introduction
　　Corder （1967） pointed that errors provided the researcher with evidence for how language was learnt and also that they served as devices by which the learner discovered the rules of the target language. Thus， in the teaching of English writing， teachers can take the errors as the feedback of students’ learning and then find out the shortcomings which need further attention.
　　The present study examines some common and frequent errors occurred in students’ English writings， and the description and causes analysis of these errors would provide teachers and students some pedagogical implications and further attention to the following teaching and study. The participants of this study are non-English sophomores， who were asked to write an English argumentative composition about 150 words on the topic of computer within 40 minutes.
　　2. Error types
　　2.1 Misuse of Singular or Plural Form of Nouns
　　The errors in singular or plural form of nouns are the most frequent one in all of errors. This type of error accounts for 19% in all of the 17 error types. Misusing of singular or plural form of nouns means that the students may know the spelling of the nouns， but neglect to change the form of the nouns. Some of the examples from the sample writings are as follows：
　　a） Computer brings about many change to our world. （changes）
　　b） The computers have many function. （functions）
　　c） Students use their owner computer to play computer games. （own computers）
　　d） Computer is a very important and common things for us. （thing）
　　The reasons of this type of error can be classified as two kinds. On the one hand， students may do not know whether the noun is a countable noun or uncountable noun （example a b）. On the other hand， some students commit this type of errors as the result of neglecting of the agreement of the sentence components （example c d）.