My mother in law (from China) n my husband had a huge fight and she left the house today morning and still have not return. She also switch off her phone. She is 70 and only speaks Mandarin. Husband heck care. I dont know what to do. Should I go to the police?

Agree with all answers here... Beside police report, perhaps can print out her photo and put description and you contact then paste in some public area she likely go... That will help to locate her if someone happens to see. Can try contact her friends too if you know some...