Based on emergy theory and synthesis method, and investigation data of typical rice planting farmers in Huiyang District, Huizhou City of Guangdong Province as the case, an ecological economic evaluation and comparison was made on farm cattle system and pint-size tractor system which are two kinds of typical agro-traction system in China, from resources structure, transfer and production efficiency, environment loading and sustainability. The emergy based accounting function of mechanical motivity was optimized, and a new emergy transformity of tractor motivity was given out based on this study. Some of their emergy indices were compared with those of horse and tractor in Swedish agricultural system. The result shows that farm cattle system consumes 4.57 times' non-renewable resources and 6.14 times' labor resource that of tractor system on unit rice paddy. Compared with tractor traction, the output impetus of farm cattle is on a lower level in the energy hierarchy. The ELR of cattle traction is only 24% of the tractor system, and its ESI is 4.25 times that of tractor system, while the current energy efficiency of cattle traction in plough production is only 3% that of tractor impetus, and 1.98% that of horse system in Swedish agricultural system. That means there is large room to improve the efficiency of farm cattle traction. The efficiency of use pint tractor traction in Guangdong rice paddy is higher than that of 65 kW tractor system in Swedish agricultural system. To improve emergy efficiency, there is much more space to optimize farm cattle traction system than pint tractor traction system, by decreasing extra labor cost and increasing the use efficiency of its tractor output. Labor and maintenance cost during the production and use process of tractor were unneglectable emergy input of tractor system.