Exhibit 5.1

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Gridsum Holding Inc.

South Wing, High Technology Building

No. 229 North 4th Ring Road

Haidian District, Beijing 100083

People’s Republic of China

22 January 2019

Dear Sirs

Gridsum Holding Inc.

We have examined the Registration Statement on Form S-8 to be filed by Gridsum Holding Inc., a Cayman Islands exempted company incorporated with limited liability (the “Registrant”), with the Securities and Exchange Commission (the “Registration Statement”), relating to the registration under the Securities Act of 1933, as amended, of 1,314,257 Class B ordinary shares, par value US$0.001 per share, of the Registrant (the “Shares”) for issuance pursuant to the Gridsum Holding Inc. Equity Incentive Plan (the “Plan”), pursuant to the provisions of the Plan providing for an automatic increase in the number of shares reserved for issuance thereunder.

As Cayman Islands counsel to the Registrant, we have examined the corporate authorisations of the Registrant in connection with the Plan and the issue of the Shares by the Registrant and have assumed that the Shares will be issued in accordance with the Plan and the resolutions authorizing the issue.

It is our opinion that the Shares to be issued by the Registrant have been duly and validly authorised, and when issued, sold and paid for in the manner described in the Plan and in accordance with the relevant resolutions adopted by the Board of Directors of the Registrant (or any committee to whom the Board of Directors have delegated their powers with respect to administration of the Plan) and when appropriate entries have been made in the Register of Members of the Registrant, will be legally issued, fully paid and nonassessable.

We consent to the use of this opinion as an exhibit to the Registration Statement and further consent to all references to us in the Registration Statement and any amendments thereto.

Yours faithfully

/s/ TRAVERS THORP ALBERGA

TRAVERS THORP ALBERGA