what is invitation letter how i can make it is it important for visit visa

Are you going to China for leisure purpose? If so, you may only get a single-entry L visa with a duration of stay for 30 days. But you can extend it before it expires within China for at most two times, each time allowing another 30 days of stay.
The L visa requirements include: your passport and one recent passport photo; visa application form V2011A and V2011B; your UAE resident visa; copies of the data pages of the applicant's passport and UAE resident visa; a no-objection letter from the your company stating your position ,monthly or yearly salary; invitation letter from the applicant's relatives from China with a Copy of the relative's ID card or passport & residence visa. The invitation letter should contain the applicant's name, passport number, purpose of travel and the invitor's basic info, etc.