Its your fault can be translated as 是你的错 in Chinese. It is pronounced as 'shì nǐ de cuò' in mandarin.
你的 (nǐ de) means your
错(cuò) means fault
so 你的错 (nǐ de cuò) means your fault

If you want to say 'its all your fault' , you can add 都 -- 都是你的错 (dōu shì nǐ de cuò)