This paper aims to study the unique interlanguage phonological system of the L 1 Cantonese learners of English in Guangdong Province,including the roles of the differences between native language and target language,language transfer and other constraints during the interl.anguage formation process.An experiment has been designed to test the pronunciation of targeted consonants of the vocational college students,who are English majors with Cantonese as native language but are also exposed to Mandarin for a long time.Resuits show that the sounds that do not exist in native language are easily pronounced incorrectly.Tbe phonological system the subjects develop to substitute the targeted consonants is quite different from that of the L 1 Cantonese learners from Hong Kong and is also varied from that of the L1 Mandarin learners from other province of mainland China.It confirms that the L1 Cantonese learners of English in Guangdong Province do have a unique phonological system in their interlanguage and that special attention should be paid by teachers during the teaching of English pronunciation.