The Commission said competition in the wind industry would not be affected by the merger of the two major OEMs.
The combined resulting company would have an approximate market share of 13% - becoming the second largest in the world, behind Vestas, according to 2016 figures from FTI Consulting.
"The onshore wind turbine market is rather fragmented with several large competitors even after the merger," the competition department said.
"The offshore wind turbine market is more concentrated with Siemens and MHI Vestas being the main competitors. Gamesa is also active in the market through its subsidiary Adwen.
"However, as the investigation confirmed that Adwen is not a competitive constraint on Siemens, it is unlikely that the transaction will appreciably change the competitive situation," it added.
US anti-trust authorities sanctioned the deal in February.
The merger was first announced in June 2016, after months of negotiations. Siemens will acquire a 59% stake in the company, with Gamesa owning the remaining 41% — 8% of which will be owned by Spanish developer Iberdrola.
Gamesa's shareholders approved the deal in November 2016.
Completion of the merger is expected to take place by early April, Gamesa said.