Airborne colocated multiple-input multiple-output (C-MIMO) radar system has been validated to offer improved multitarget tracking (MTT) capabilities. By combining the beampattern design and observation position optimization of airborne C-MIMO radar with traditional resource allocation strategies, higher degrees of freedom can be obtained, leading to resource utilization efficiency and performance enhancements. In this article, a joint beampattern design and online route planning (JBD-ORP) strategy is proposed for MTT in airborne C-MIMO radar system under jamming environments. The key mechanism of the proposed strategy is to collaboratively coordinate the waveform correlation matrix (WCM), kinematic velocity and heading angle of the airborne radar, in order to improve MTT performance under the constraints of maneuverability limitations and system resource budgets. The predictive Bayesian Cramér–Rao lower bound is derived and adopted as the metrics to characterize the target tracking accuracy performance. As the formulated JBD-ORP problem is nonlinear and nonconvex, we approach it differently depending on whether prior information about interference source is known and propose a partition-based three-stage approach to solve it effectively. Simulation results show that the proposed JBD-ORP strategy achieves the best system performance in comparison with other benchmarks.