Battery-electric-bus(BEB) is the breakthrough to promote the development of new energy vehicles. This paper aims to optimize the BEB operation mode, measure subsidies efficiency and anticipate the subsidy time to speed up the marketization of battery-electric-bus. At first, the BEB system has been abstracted and a satisfaction model with almost all the factors has been established to reflect the inter relationships. By the analysis of Hefei NO.18 bus line, a BEB demonstration line in China, we get conclusions that NO.18 bus line is suitable for Slow Charging Mode rather than Battery Leasing & Displacing Mode and the subsidy to NO.18 bus line is appropriate. Then the reliance of subsidies on battery cost is discussed. Considering the progress of battery technology and decrease of battery cost, Subsidies should be reduced appropriately over time. It is demonstrated that when the cost degrades by 60%, operators will profit even without any subsidies under the market mechanism and it is anticipated that BEB marketization will be realized in the next decade with strong and sustaining policies support from the government.