In recent years, ITM 399 series tractor has been manufactured in Iran Tractor Manufacturing Company (ITM), which can be suitable for small farms operations. For big farms operations, minimizing energy consumption, decreasing the time losses and increasing work efficiency, a heavy duty tractor of ITM 8200 series was started to design in the same Company. The gearbox selection, design and analysis for this tractor with the engine power of 154 horse power is studied in this research. The mechanical gearbox equipped with mechanical-hydraulic dynashift system was used in ITM 8200 power transmission system. The dynashift system produces four cases (A, B, C and D) with 8 speeds that produced by main gearbox, which altogether produces 32 forward speeds and 32 reverse speeds for this new tractor. To design the gearbox, with recommended speeds, gearbox ratios and gears ratios was calculated. Then by using the engine torque and slip torque on tractor gearbox, the exerted loads on gears were calculated. After this, by using of American Gear Manufacturing Association (AGMA) method and computer programming design, the gears have been designed. Finally one of the gears in ANSYS software analyzed. The results of this analysis show that: The gears have been designed for tractor gearbox can endure loading and transfer the power requirement of new tractor. The design safety factor of gears has been obtained by ANSYS software approximately equals with safety factor of AGMA methodology. In gear analysis, for applying load to one of gear tooth (unit contact ratio), stress distribution will produce in gear body and especially on neighboring teeth body. For tractor gearbox design, it would be necessary to include slip torque, which will decrease the gear width and gearbox volume.