Ms Harman suggested Mrs May looked like she was “begging for a trade deal” when she briefly held hands with the United States president as they walked from the Oval Office to a press conference.
The Labour former cabinet minister joined the calls for Mrs May to cancel Mr Trump’s state visit to the UK, planned for this year but facing a backlash following his controversial travel ban affecting seven mainly Muslim countries.
Mr Trump has been involved in a string of controversies during his time in politics, including his suggestion that his fame allowed him to grab women “by the pussy”.
Ms Harman highlighted those comments as she discussed the PM’s visit to Washington DC.
Speaking on BBC One’s Graham Norton Show, Ms Harman said: “She (Mrs May) has got to look like a strong prime minister of a strong self-confident country and not look like she’s begging for a trade deal on any terms.
“She needs to stand up for herself and our country.
“That’s why that hand-holding thing was so disastrous because it looked like he was leading her along.
“There are all sorts of rumours as to why he did it but I think she should have had in her briefing, ‘This man is a identified groper - stand well away!’”