Abstract: Under the “wheat/maize/sweet potato” tri-crop intercropping system in the southwest China, we researched into the effects of different straw mulching treatments on root morphology, physiological characteristics of transplanted maize at seedling stage. Taking local traditional farming (T) as CK, the other two treatments were straw mulching (TS) and straw mulching plus decomposition catalysts (TSD). The entire experiment lasted for two years. Results show that straw mulching moderately increases root length and root surface area, while significantly increasing root length within 1.0~2.5 mm diameter compared with T treatment. However, there is no significant difference between TSD and TS treatments. Significantly increases in maize seedling root vigor by respectively 19.12%, 27.46%, in root-shoot ratio by 36.72%, 37.50%, and in root biomass by 62.53%, 69.42% are noted under TS and TSD treatments for 2008. Compared with T, the above indicators increase respectively by 17.86% and 25.83%, 31.54% and 33.08%, 65.69% and 77.37% for 2009. Meanwhile, straw mulching enhances soil moisture and nutrient supply. Straw mulching conservation tillage enhances root development and other physiological characteristics under maize intercropping system at seedling stage by changing farmland environment. Straw mulching with decomposition catalysts even performs better.