Five carriages derailed from the Tsunami ride at the site in Strathclyde Country Park in Motherwell, North Lanarkshire, on Sunday June 26.
Emergency services rushed to the scene and 10 people, including eight children, were taken to hospital for treatment to serious head, leg and arm injuries.
The Health and Safety Executive (HSE) joined police in investigating the incident and last week issued a prohibition notice banning the safety inspector who had approved the Tsunami before its crash.
The Tsunami will remain closed but M&D’s said all other rides have been tested and the reopening of the park approved by HSE.
A spokesman said: “All of the rides have undergone thorough independent testing and, following dialogue with the HSE, the theme park has now reopened to our customers.
“Safety remains our paramount concern and each and every ride will continue to be safety-checked on a daily basis.
“The Tsunami remains closed until further notice.”
The theme park apologised earlier this week after a billboard for a new ride carried the phrase ‘bring on the fear’.
The advert for the Giant Condor ride appeared on a street in Hamilton, South Lanarkshire, just weeks after the Tsunami derailment.
An M&D’s spokesman said: “All of our planned advertising campaigns were cancelled in the immediate aftermath of the Tsunami accident.
“An error by our billboard advertising agency ClearChannel resulted in this advert appearing on a single site.
“We ordered its removal as soon as we were alerted to it and ClearChannel has assured us that its mistake will not be repeated.
“We would like to apologise for any distress caused.”
According to the M&D’s website, The Giant Condor is the only one of its kind in Europe.
The advert says: ‘’You can soar into the sky to over 30 metres in 28 custom-built gondolas built for two. It’s big, it’s very scary, it’s The Giant Condor.’’