Abstract: Runoff renewability is an important topic in the study of water cycle, and the knowledge of it is important for sustainable utilization of water resources in arid and semi-arid climate areas. Based on hydrological and meteorological data and the information related with human activity including soil and water conservation and water diversion, and using statistical method, we have studied the temporal variation in runoff renewability (I_rr) and its formative cause in the middle Yellow River basin. We found that at the time scale of 59 year, I_rr shows a decreasing trend superposed by some secondary fluctuations, which divides the variation into four stages. Although the correlations of I_rr with three climate variables in the same year such as annual precipitation (P_m), air temperature (T_m) and summer monsoon intensity (SMI) are relatively low, we found significant time-lag effect of the variation in P_m, T_m and SMI on I_rr, based on which the characteristic length of time-scale (L_t) can be determined. The correlation coefficients of I_rr with N-year moving averages of a climate variable were calculated and then plotted with N. TheNassociating with the turning point is determined as L_t. We found that the L_t for the influence of P_m, T_m and SMI on I_rr are 11, 9 and 4 years respectively. There is close negative correlation between I_rr and the area of each type of soil and water conservation measures, and the total area. The large-scale implementation of ecological restoration centering on“conversion of degraded farm land into forest and grass land ”since 1998 has resulted in a further reduction in I_rr. A regression equation between I_rr and the index (I_wd,5m) of warming and dryness and the total area (A_sw) of soil and water conservation measures was established which indicates that I_rr decreases with I_wd and A_sw.