The interjection 哎呀
An interjection (感叹词) is a word or expression that occurs as an utterance on its own and expresses a spontaneous feeling or reaction. It expresses feelings and emotions but does not name them. It is usually placed at the beginning of a sentence.
哎呀 
can express many different emotions:
1) strong feelings of pain, fear or suffering. It can be translated as "ouch", "oh, my".
can express many different emotions:
1) strong feelings of pain, fear or suffering. It can be translated as "ouch", "oh, my".Examples
哎呀，难受死了！
Ouch! it hurts so bad!
āiyā, nánshòu sǐ le
哎呀，快一点，他摔倒了！
Oh my! Come faster, he fell down!
āiyā, kuài yìdiǎn, tā shuāi dǎo le
2) admiration. Can be translated as "whoa!", "wow!".
Examples
哎呀，这里那么美啊！
Whoa, it’s so beautiful here!
āiyā, zhèlǐ nàme měi a
哎呀，你的姐姐那么漂亮！
Wow, your sister is so beautiful!
āiyā, nǐ de jiějie nàme piàoliang
3) surprise. You can translate it as "oh!", "hey!".
Examples
哎呀，蚊子太多了！
Oh! There’s so many mosquitoes!
āiyā, wénzi tài duō le
哎呀! 竟然在这里碰上了你
Hey! How unexpected it is to meet you here!
āiyā! jìngrán zài zhèlǐ pèngshàng le nǐ
4) regret and doubt. Can be translated as "ugh", "man".
Examples
哎呀! 我这是干了些什么呀！
Ugh, what have I done!
āiyā! wǒ zhè shì gàn le xiē shénme ya
哎呀，现在如何再次相信他？
Man, how can I trust him again?
āiyā, xiànzài rúhé zàicì xiāngxìn tā
5) When suddenly remembered something. You can translate it as "oh".
Examples
哎呀，今天是哥哥的生日！
Oh, today is my brother's birthday!
āiyā, jīntiān shì gēge de shēngrì
哎呀, 我忘记打开手机了！
Oh, I forgot to turn on my phone!
āiyā, wǒ wàngjì dǎkāi shǒujī le
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