Abstract: Based on both the NCEP/NCAR reanalysis data and the observed rainfall data, the results show that summer precipitation conversion rate of the whole layer over the Yellow River basin is relatively low. This considers that there should be a certain pressure level which has the most favorable conditions of water vapor transportation, lifting condensation and vertical motion during the entire layer. Thus, this pressure level is defined as the layer of effective precipitation conversion rate (referred to as the effective layer), and the ratio of precipitation to the effective layer's precipitable water is called the effective precipitation conversion rate. Through analyzing the average factors such as vertical velocity and water vapor in every subarea, the summer effective layers of the upper, middle and lower reaches are identified as ground -500 hPa, 600-400 hPa and 850-600 hPa, respectively. It's proven that the evolutional trends of summer mean water budget and precipitation conversion rate in the whole layer and in effective layer are consistent, peak and valley corresponding, and the values of precipitation conversion rate of the effective level are greater than that of the whole layer during the whole 49 years. The summer effective precipitation conversion rate reaches the highest over the Tibetan Plateau and the eastern part of the middle Yellow River but the lowest over the northeast side of Tibetan Plateau separately. Its distribution forms are similar in drought/flood years and multi-year mean, while the values in flood years are significantly higher than those in drought years.