Edna Atherton was 88 when she fell from the platform, suffering broken ribs and a cut head at Birkenhead's Hamilton Square station in July 2015.
The prosecution had claimed Martin Zee, 33, had not followed Merseyrail's door closure safety procedure fully.
But the defence argued the fall was an accident, Liverpool Crown Court heard.
They said there was a "fundamental failing" in the 17-point safety procedure itself, because the curve of the platform meant there were several blind spots.
The trial was shown CCTV footage of Mr Zee leaving the back of the train and walking to the wall of the platform to check all passengers had got off and on the carriages.
After Mr Zee pushed the button to close the doors, two women can be seen trying to board the front of the train. As the doors were reopened and closed, one of them fell between the train and the platform.
Mr Zee, of Coronation Road, Runcorn, Cheshire, had pleaded not guilty to a charge of endangering the safety of railway passengers by wilful omission or neglect.
The jury cleared him after two hours of deliberations.
A Merseyrail spokesman said its internal investigation and another by safety regulator the Office of Rail and Road "found there was no case to answer".
"The door closure warning alarm is in place to alert passengers to the danger of closing doors and we rely on passengers heeding that warning and not attempting to board or alight while the doors are closing."
A spokesman for British Transport Police said: "It is our duty as a police force to investigate and present the evidence to the Crown Prosecution Service."
A Crown Prosecution Service spokesman said: "The decision to charge was made following detailed consideration of the evidence and in accordance with the Code for Crown Prosecutors."
A railway guard has been cleared of endangering passenger safety after an elderly woman fell between a train and a platform.