The development of a new side-sliding discharge scheme can provide efficient uniform ultraviolet (UV) preionization for transverse excitation (TE) CO2 laser. The use of the scheme has resulted in the successful generation of CO2 laser discharges between electrodes separated by 5.5 cm, total cross section is 27.5 cm2. The laser is modular in construction, under the condition of V(CO2)∶V(N2)∶V(He)=1∶1∶4 mixtures and 60 kPa gas pressure, a modular with active discharge volume 5.5 cm×5 cm×90 cm has yielded output energy of 53 J, the specific output energy ratio is 3.46×10-4 J/(L·Pa). When a pair of discharge modulars are employed in series in a simple oscillator configuration, output energy of 103 J is yielded. An effect of laser energy enhancement occurs in dual-modular, the output energy of dual-modular is 15% higher than twifold energy of single modular.