在分析农户使用、更新小型拖拉机经济行为的基础上,推证并建立了户营小型拖拉机的作业成本随使用年限增加而变化的规律,进一步提出户营小型拖拉机在作业量充足条件下的“成本均等理论”和在作业量欠充足条件下的“成本递减理论”,并通过实地采样加以验证。据此阐述了户营小型拖拉机难以更新的机理,得出在经济欠发达地区户营小型拖拉机基本上不存在最佳更新期的结论。 On the basis of analyzing the use of peasant household and updating economic behavior of small tractor, the law that operating cost of small household tractor is changing with the increase of service life is deduced and established. It is further proposed that the cost of small household tractor under the condition of adequate working load Equal Theory “and” Cost Reduction Theory "in the case of insufficient workload, and verified by field sampling. Based on this, the mechanism that small-scale tractors in Huying battalion can not be renewed is expounded, and the conclusion that there is basically no best regeneration period exists in Huizhou small-scale tractors in economically underdeveloped areas.