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You have a problem, but I can suggest little more than practice and concentration; I presume you have a tutor or teacher or acquaintance who can listen to and advise you. I hadn't noticed that Chinese students have much trouble with vowel sounds before-- I thought the consonants were more difficult.
While there are plenty of regional variations in English pronunciation, the pronunciation of e.g. the /e/ in
egg is usually similar enough to elude the sensitivities of a learner. Practice saying and listening to (pronunciations are available at
MERRIAM-WEBSTER ONLINE, for example) lots and lots of simple words with those vowel sounds:
apple, cram, fat, hat, rat, sat and bat, etc.
egg, eft, end, bend, send, fend, rend, et cetera.by, sigh, guy, rye, die, fry, sky, etc.