EXHIBIT I

JOINT FILING AGREEMENT

This will confirm the agreement by and among the undersigned that the Schedule 13G filed with the Securities and Exchange Commission on or about the date hereof with respect to the beneficial ownership by the undersigned of Ordinary Shares of 21Vianet Group, Inc. is being filed, and all amendments thereto will be filed, on behalf of each of the persons and entities named below in accordance with Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended. This Agreement may be executed in two or more counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument.

Dated: February 6, 2013

MATRIX PARTNERS CHINA I, L.P.
By:	Matrix China Management I, L.P.
By:	Matrix China I GP GP, Ltd.

By:	/s/ David Su
Name:	David Su
Title:	Director

MATRIX PARTNERS CHINA I-A, L.P.
By:	Matrix China Management I, L.P.
By:	Matrix China I GP GP, Ltd.

By:	/s/ David Su
Name:	David Su
Title:	Director

MATRIX CHINA MANAGEMENT I, L.P.
By:	Matrix China I GP GP, Ltd.

By:	/s/ David Su
Name:	David Su
Title:	Director
MATRIX CHINA I GP GP, LTD.
By:	/s/ David Su
Name:	David Su
Title:	Director

/s/ Yibo Shao

YIBO SHAO