China's local government debt financing grows rapidly featuring surging chengtou bond issuance and risk exposure since the global financial crisis in 2008. The accumulation of local government debt poses systemic risks to China's fiscal and financial systems. Using weekly data from 2009 to 2014, this paper studies the joint dynamics and risk transmission mechanism between chengtou bond spreads and treasury yields under the framework of the extended no-arbitrage Nelson-Seigel term structure model, which guarantees the no-arbitrage relationship between treasury yields of different maturities. The results show that the chengtou bonds indeed exhibit considerable local risks and can lead to systemic risk of the treasury bonds, such that the treasury yields have significant component of risk premium due to chengtou risk. On the other hand, as the safest asset in China at present, the treasury yields with short-to-medium maturities decrease as a result of the “fly-to-safety" effect when the chengtou risk increases. Meanwhile, the dynamics of chengtou bond spreads reflect the market-oriented risk pricing by investors on credit and liquidity risks under limitations of the government implicit guarantee. Under this condition, it is the right timing to reasonably standardize and institutionalize the local government bond market with transparent market mechanism.