You can visit this webiste https://www.travelchinaguide.com/embassy/visa/marriage-registration.htm for the procedure of Marriage Registration in China.

You can apply for L visa, you should submit:
(I) Original passport with validity more than six months and minimum 2 blank visa pages;
(II) Photocopy of the first 2 pages (personal information) of the passport and the recent Chinese visa page if there is any;
(II) One fully completed visa application form in Chinese or English, attached with one of the applicant's recent color photograph (30mm X 40mm)
(III) Invitation letter from your relative you want to visit
(IV) ID card copy or passport copy of your inviter or household copy of your girlfriend.