It rose above 40 per cent in 18 weeks since the first week of March, according to the Realmeter survey.
The negative assessment on Moon's conduct of state affairs declined 3.2 percentage points from a week earlier to 54.9 per cent last week, reports Xinhua news agency.
Support for Moon's ruling Democratic Party advanced 3.3 percentage points to 32.9 per cent.
The main conservative opposition People Power Party garnered 37.1 per cent of approval score last week, down 0.6 percentage points from the previous week.
The minor centre-left Open Democratic Party won 7.0 per cent of support, trailed by the minor centre-right People's Party with 6.0 per cent and the minor progressive Justice Party with 3.5 per cent, respectively.
The result was based on a survey of 2,519 voters conducted from July 5 to 9.
It had plus and minus 2.0 percentage points in margin of error with a 95 per cent confidence level.