The 2018 Thai League T4 (also known as the Omsin League for sponsorship reasons) was the 18th season of the Thai League 4; it had redirected from the regional league division 2, since its establishment in 2006. The 60 clubs will be divided into six groups (regions). The 15 clubs advance to the Champion league round.
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<span style="color:Red;">Red Zone : 2018 Thai League 4 Bangkok Metropolitan Region</span><br> <span style="color:Yellow;">Yellow Zone : 2018 Thai League 4 Eastern Region</span><br> <span style="color:Pink;">Pink Zone: 2018 Thai League 4 Western Region</span><br> <span style="color:Green;">Green Zone: 2018 Thai League 4 Northern Region</span><br> <span style="color:Orange;"> Orange Zone: 2018 Thai League 4 North Eastern Region</span><br> <span style="color:Blue;">Blue Zone: 2018 Thai League 4 Southern Region</span>
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3rd place from each zone of 2018 Thai League 4 have signed to qualifying in this round. Preliminary round 1 will be started after finish all matches of all zone by FA Thailand.
The qualifying round will be played in regions featuring clubs from the 2018 Thai League 4 Northern Region, 2018 Thai League 4 North Eastern Region and 2018 Thai League 4 Eastern Region
The qualifying round will be played in regions featuring clubs from the 2018 Thai League 4 Western Region, 2018 Thai League 4 Bangkok Metropolitan Region and 2018 Thai League 4 Southern Region
Runner-up and 3rd place from each zone of 2018 Thai League 4 and winners from Preliminary round 1 have signed to qualifying in this round. Play-off round will be started after finish all matches of Preliminary round 1 by FA Thailand.
9 automatic Thai football teams and Winner teams from Play-off round pass to this round. this round provide 2 part to 2018 Thai League 4 champions league round Upper group and 2018 Thai League 4 champions league round Lower group. Each region has 6 Thai football teams. It plays Round-robin matches. Thai football teams which get champion and runner-up which has the best scores of each region to were promoted to 2019 Thai League 3. Mini-league rule is used to this tournament.
Runner-up of Upper group and Lower group in Group Stage round pass this round. Winner of Third place play-off round was promoted to 2019 Thai League 3.
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Champion of Upper group and Lower group in Group Stage round pass this round. Winner of Champion round get champion of 2018 Thai League 4
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the best