The structure design of the high precision and high dependability multi-beam lasers combining beam and extending beam is very important in the engineer appliance. Under this background, the fission foundry benchmark flat was advanced. The brief, middle and long wave band lasers were set in a little box whose length, width and height were 1 280 mm、990 mm、815 mm. And this box can be adjusted on space position. The main body structure of laser combining beam and extending beam were designed. At the same time, some important parts were analyzed by using the finite buck statics software. The adjusting mete of the angle on the laser outgoing direction in the flat is bigger than ±30′, and the flatchief mass is about 600 kg. Under the precondition that the transition benchmark flat system bearing the weight of the flat load, its maximum deformation strain meeting an emergency is 0.005 mm. It can be indicated that this structure can satisfy this kind laser combining beam and extending beam and adjusting request in small space. This method can be extended to other light way about combining beam and extending beam structure design.