In a long-term planning for neutrino experiments in China, a medium baseline neutrino beam is proposed which uses a continue wave(CW) superconducting linac of 15 MW in beam power as the proton driver. The linac will be based on the technologies which are under development by the China-ADS project, namely it is also composed of a3.2 Me V normal conducting RFQ and five different types of superconducting cavities. However, the design philosophy is quite different from the China-ADS linac because of the much weaker requirement on reliability here. The nominal design energy and current are 1.5 Ge V and 10 m A, respectively. The general considerations and preliminary results on the physics design will be presented here. In addition, the alternative designs such as 2.0 Ge V and 2.5 Ge V, which may be required by the general design, can be easily extended from the nominal one. In a long-term planning for neutrino experiments in China, a medium baseline neutrino beam is proposed which uses a continue wave (CW) superconducting linac of 15 MW in beam power as the proton driver. The linac will be based on the technologies which are under development by the China-ADS project, which it is also composed of a 3.2 Me V normal conducting RFQ and five different types of superconducting cavities. However, the design philosophy is quite different from the China-ADS linac because of the much weaker requirement on reliability here. The nominal design energy and current are 1.5 Ge V and 10 m A, respectively. The general considerations and preliminary results on the physics design will be presented here. In addition, the alternative designs such as 2.0 Ge V and 2.5 Ge V, which may be required by the general design, can be easily extended from the nominal one.