Do i need invitation letter from my father to get saudia arabia visa?

You need the following documents to apply for a Saudia Arabia family visit visa from the Embassy of Saudi Arabia in China:
1. A passport valid for at least six months, with at least two (2) clear visa pages adjacent to each other.
2. One recent passport size color photograph with a white background.
3. A completed application form filled-out with a black ink pen or printed.
4. your birth certificate
5. If you are under 18 years old and will travel alone, you must submit a notrized letter of authorization, in either in Arabic or English, signed by both parents or legal guardians.
6. A reference note showing the number and the date of the visa issued by the Ministry of Foreign Affairs or any of its branches in Jeddah or Dammam.
7. your residence permit in China