Abstract
Nowadays, the studies on the language transfer are more concerning the impact of Chinese language on English learning. Very few of them are on the phenomenon of negative transfer of Tibetan language to the Tibetan students’ English learning under the trilingual(TIbetan, Chinese and English) environment. The author had a detailed analysis to the Tibetan students’ writing composition on the basis of language tranfer theories such as markedness, interlanguage hyposthesis, and etc. And figure out the main grammatical errors in their compositions through the method of Error Analysis. Contrastive Analysis is also used to have comparison among the Tibetan, Chinsed and English, and individual interview as well, the reasons for the grammatical errors are figured out. The major findings of this research are as follows: The grammatical errors emerged in the Tibetan English major students’ composition writing is in many fields, which includes omission, collocation, single and plural form of noun, subject - predicate concord, negative , possessive , relative clause and inverted sentence; Here is the reason for these grammatical errors: various thinking modes, in short of comparisons among the three languages and inadequate input. The methods can be applied to resolve are: language instructors should intsruct language learners propers through having comparison between the three languages and more importantly, strengthenging the students’ comprehensible and adequate input the learner langauge.