The solid-liquid ducted rocket (SLDR) has advantages of solid ducted rocket (SDR) as well as liquid fuel ramjet (LFR). In order to analyze the characteristics of SLDR, a mathematics model was established and several proper parameters were presented. The characteristics calculation method was presented as well. According to calculating results, the specific impulse of SLDR is higher than SDR. When the mass ratio of liquid/solid propellant reaches 1, the specific impulse can be improved 1.82 times. With excess air coefficient increasing, the specific impulse increases firstly and then decreases. At off-design conditions, the specific impulse increases and then decreases with Mach number increasing. There is a critical Mach number that makes the specific impulse to be largest and this critical Mach number decreases with flight height. The thrust coefficient increases and the specific impulse decreases with fight height increasing.