What documents should I prepare if i need to apply student visa to hong kong for 3 years?

You need to apply below documents if you want to obtain Hong Kong student visa:

Student Visa is issued to applicants who desire to go to HK for education purpose.

(1) To study in primary schools, high schools and universities, applicants are required to present the following additional documents:

a. Information of the HK school, including name, address and telephone number;

b. Enrollment Notice issued by the school;

c. Proofs of the applicant's education background, e.g. diploma;

d. If the applicant is under the age of 18, one of the applicant's parents should authorize the sponsor or his relative/friend to be the guardian of the applicant. A consent letter duly signed by both the guardian and one of the applicant's parents and the guardian should be produced;

e. Certificates of financial support, including evidence of the sponsor's financial standing, e.g. bank statements, saving account passbook, tax receipts and employment certificates; an undertaking that the sponsor is prepared to arrange accommodation for the applicant or the applicant will be staying with him; or evidence that a place has been provided in recognized boarding school;

(2) To attend in an advanced study, applicants are required to present the following additional documents:

a. Enrollment Notice issued by the HK school;

b. Certificates of financial standing and accommodation arrangement in HK;

c. Certificate of study period.