Abstract: To increase output of coalbed gas well,we have designed and drilled Lan M1-1 coalbed gas multi-branch horizontal well.With a large coalbed gas reserves,the buried depth is about 900 m.When it was being drilled,a vertical well was drilled at first,and caves were made in coalbed gas sect,then a horizontal well were drilled at a distance of 200 m,horizontal segment were in connection with the caves,and 10 branch holes were lateral drilled symmetrically in horizontal sect.Underbalance technology were taken by us during drilling,vertical hole was filled with gas,drilling fluid were mixed with gas in caves,and negative pressure drilling technology was formed.Pendulum assembly was used in vertical well and upper vertical segment of horizontal well.Steering assembly and MWD and LWD were used in main holes and branch holes of horizontal well.High viscosity drilling fluid was used for stabilizing borehole wall.Hydraulic reamer was used for making caves,and plugging at the distance of 500 m in upper vertical segment of horizontal well.A ?127mm slotted liner was hanged above vertical well cave to complete the well.The result is,total footage is 7993 m,production percentage is 100,the average mechanical rotating speed of the whole well is 8.69 m/h,percentage for making caves in segment by milling is 100, horizontal well was connected with caves only one times.Percentage for branch by impending lateral drilling in one time is 100,percentage for electric logging is 100,percentage for well completion in one time is 100.The result show that the technology for Lan M1-1 multi-branch horizontal well is advanced,and the amount of branches with 10 is the maximum in domestic market,the controlling area is the biggest in domestic market,which will provide valuable experience for domestic coalbed gas drilling in future.