A field trail was conducted to determine the effects of conventional tillage(T1), conventional tillage with stubble retention(T2), no tillage(T3) and no tillage with stubble retention(T4)treatment on crop yield and soil oxdizible organic carbon within maize-wheat-soy rotation system in the western Loess Plateau. The results indicated that there was no significant tillage effect on crop yield for each six harvesting during the year 2001 to 2004. The easily oxdizied organic carbon in the 0~5 cm soil layer under no-till with stubble retention treatment increased by 2.44 g/kg significantly compared with that under conventional treatment. The most oxdizible organic carbon had significant positive correlation to soil total nitrogen and water stable aggregates. We concluded that effect of conservation tillage on crop yield was delayed to that on soil fertility change,soil oxdizible organic carbon is a one of sensitive indicator to indicate soil organic carbon change to the tillage practice.