Abdul Abbasi was jailed for two years and four months for reversing at speed and knocking down 65-year-old Rehana Abassi on Redmire Close, Hull, in October.
The 33-year-old, of Thorndale, Hull, was convicted in March of causing serious injury by dangerous driving.
At a Court of Appeal hearing, his sentence was reduced to 16 months.
His six-year driving ban was also cut to two years by judges Sir Andrew Smith and Geoffrey Marson QC.
At his trial, heard at Hull Crown Court, Abbasi was cleared of attempted murder and causing grievous bodily harm.
The court heard the taxi driver had struck his mother as she went to the boot of the car after a disagreement.
He then crashed into a parked car some 10 to 15 metres behind him before driving off at speed with the boot still up and his mother still under the vehicle, the court was told.
Mrs Abbasi was in hospital for two weeks with serious injuries including broken ribs but has since forgiven her son, the court heard.
The court was told the jury was "not satisfied" that he knew his mother was behind the car when he reversed into her.
Sir Andrew told the court that Abbasi, who had no previous convictions and no previous record of bad driving, was "mentally fragile' and a "decent man who lost control under pressure".
Those close to him had been concerned about his mental wellbeing in the past but he had not engaged with mental health professionals.
A taxi driver who ran over his mother after an argument, causing her serious injury, has had his jail term cut.