Third party funding in international investment arbitration does not equal to third party funding in international commercial arbitration, so it is proper to make a special research on it. Disclosure is the crucial problem in regulation for third party funding. The rules of disclosure of third party funding in international investment arbitration appear to be blank and rough. In international investment arbitration, the funded party of third party funding is usually the Claimant. It is found that practice and rules cannot match through current international investment cases in relating to disclosure of third party funding. In practice, initiations of disclosure are generally by the application of the Respondent or the request of the Tribunal. The reasons that the Respondent applies for disclosure are normally the conflicts of interest and transparency. Tribunals’objections to disclosure are usually out of the consideration for the extent of disclosure. According to the comparison of practice and rules, regulating the time of requesting disclosure of the Tribunal and strictly limiting the extent of disclosure might be the applicable method to promote the regulation of disclosure of third party funding in international investment arbitration.