The tournament will be divided into 12 sub-regions with 3 stages in each sub-regions. Qualification stage: This method will be applied when there are more than 8 clubs in a sub-regions. This can be both one-legged knock out or round-robin basis depend on amount of participated clubs in the sub-regions. Group stage: This round divided 8 qualified clubs into 2 groups and play in single round-robin. Only the group winners will qualified to the next stage. Final stage: The groups winners play against each other in one-legged match. The winners of the sub-region will play in the regional final against the winner from another sub-region which is in the same region to decide the club to promote to 2020 Thai League 4. 30-minute extra time and penalty shoot-out will be applied after the match is still in tie respectively.
Upper northern subregion
Qualification stage
Group A1 Group A2 Group A3 Group B1 Group B2 Group B3 ----
Group stage
Group A Group B The actual result is a 2-2 draw, but Singh Nuea Chiang Mai was 0-2 forfeited due to fielding an ineligible player.
Lower northern subregion
Play-off round
Qualifying round
Group A1 Group A2 Group A3 * Northern Tak United won the first place of the group due to better disciplinary points than PL Tech Pitsanulok. Group A4 Group B1 Group B2 Group B3 Group B4 ----
Group stage
Group A Group B
Upper northeastern subregion
Play-off round
Qualification round
Group A1 Group A2
The match between Roi Et 2018 and Takhon City is cancelled due to Takhon City didn't show up at the match.
Group A3
Group A4 Group B1 Group B2 Group B3 Group B4 ----
Group stage
Group A Group B
Lower northeastern subregion
Play-off round
Qualifying round
Group A1 Group A2 Group A3 Group A4 Group B1 Group B2 Group B3 Group B4 ----
Group stage
Group A Group B
Upper eastern subregion
Qualifying round
Group A1 Group A2 Group B1 Group B2 ----
Group stage
Group A Group B
Lower eastern subregion
Qualification round
Group A1 Group A2 Group B1 Group B2 ----
Group stage
Group A Group B
Bangkok Metro
Play-off round
Qualifying round
Group A1 Group A2 Group A3 Group A4 Group B1 Group B2 Group B3 * Royal Thai Army Headquarters withdraws, so all match which involves Royal Thai Army Headquarters is cancelled, and Phoenix F.C. qualified to the next round. Group B4 ----
Group stage
Group A Group B
Perimeter region
Qualification stage
Group A1 Group A2 Group A3 Group B1 Group B2 Group B3 ----
Group stage
Group A Group B
Upper western subregion
Qualification stage
Group A1 Group A2 Group A3 *Samut Sakhon Warriors withdraw, so all match which Samut Sakhon Warriors will play is cancelled. ** Saraburi Warriors is forfeited due to fielding ineligible players at the match, the actual result is 2-1 to Saraburi Warriors. ---- Group B1
Group A1 Group A2 Group A3 Group B1 Group B2 *Samut Sakhon City withdraws, so all match which include Samut Sakhon City is cancelled, and KU Kampang San qualified to the next round. Group B3 ----
Group stage
Group A Group B
Upper southern subregion
Qualifying round
Group A1 Group B1 *Surat Thani United withdrew, so Plai Phraya City and Khun Thalay SRU qualified to group stage. ----
Group stage
Group A Group B
Lower southern subregion
----
Group stage
Group A
Group B
Subregional final
The actual finalist Singha Nuea Chiang Mai was 0-2 forfeited by JT due to fielding an ineligible player.
Final
Northern region
Northeastern region
Eastern region
Bangkok & fields region
Western region
Southern region
Championship stage
Group A
Group B
Final
Promoted clubs
According to FA Thailand's declaration about promoting clubs to the 2020 Thai League 4 by considerate amount of participate clubs in each regions, FAT revealed that there will be 9 clubs to promote to the next season of T4 League.
