Valuing ecosystem services (ES) is helpful for effective ES management. However, there are 2 many limitations in traditional ES valuation approaches, including theoretical challenges and 3 practical difficulties. To overcome these limitations, we proposed a dual value system (DVS). And 4 then, we presented a case study of valuing the water provision in Zhujiang River Basin (Pearl 5 River Basin) based on DVS. DVS follows the axioms that (1) human life would end if we lose any 6 of vital ES which is indispensable to human being's survival (such as oxygen, freshwater) and (2) 7 ES cannot provide any value to people without human activities. Correspondingly, DVS includes 8 two types of value: the output support value (OSV) of a vital ES refers to the total value produced 9 by human being's economic and social activities (TVPH) supported by the ES consumption; the 10 optional capacity value (OCV) of a vital ES refers to the optional capacity of supporting TVPH 11 provided by total ES volume. The OCV provided by a vital ES is calculated by using the product 12 of multiplying the OSV (TVPH) by the freedom of choosing the consumption from the total 13 volume of this ES, valued in non-monetary units. Based on DVS, the OSV and OCV of water 14 provision in Zhujiang River Basin were analyzed in river basin scale and sub-basin scale, and the 15 values variation of water provision from 2006 to 2015 was analyzed in sub-basin scale. And then, 16 based on this case study, we discussed the new insights into ES provided by DVS. Results proved 17 that DVS and its assessment scheme overcame the limitations on current ES valuation approaches 18 and provided an innovative quantitative framework to understand and value ES which will help to 19 make good decisions in ES management. 20 21 Keywords 22 Ecosystem services valuation; dual value system; output support value; optional capacity value; 23 ecosystem services spatial subsidy; Pearl River Basin 24 25 ES: ecosystem service(s) OSV: output support value OCV: optional capacity value DVS: dual value system GDP: gross domestic product TVPH: total value produced by human being's economic and social activities PRWRC: Pearl River Water Resources Commission of the Ministry of Water Resources 466 Modeling the dynamics of the integrated earth system and the value of global ecosystem services 467 using the GUMBO model. Ecol Econ, 41: 529-560 https://doi.476 Paruelo J, Raskin R G, Sutton P, VandenBelt M. 1997. The value of the world's ecosystem services 477 and natural capital. Nature, 387: 253-260 https://doi.