Pulse jamming is a kind of well-used active jamming against airborne pulse-Doppler radar. In this paper, the time-frequency characteristics of the pulse jamming are studied and a novel anti-jamming method is proposed based on joint time-frequency analysis for the airborne radar working in the frequency-modulated ranging (FMR) mode. Based on the time-frequency analysis on measured radar echoes, the pulse duration and other important parameters can be estimated via joint time-frequency analysis and the merged targets under jamming can be effectively detected accordingly. Finally, the numerical experiments are provided to demonstrate the performance of the proposed method.