The 2017–18 Southern Combination Football League season was the 93rd in the history of the competition, which lies at levels 9 and 10 of the English football league system.
Of the fourteen runners-up, the twelve clubs with the best PPG (points per game ratio) were also to be compulsorily promoted, but with resignations and mergers in leagues above, thirteen runners-up were promoted.
Division One featured 16 clubs which competed in the division last season, along with two new clubs, relegated from the Premier Division: Step 6 clubs without ground grading Grade G were to be relegated to Step 7, but no club in this division failed the ground grading process.
All Step 6 leagues were fixed at a maximum of 20 clubs for 2018–19.
Promotion from this division depended on ground grading as well as league position.