A traffic flow detection-based LED alarm lamp includes a red LED device, a blue LED device, an alarm lamp leg, a mounting assembly and a reinforcing plate. The red LED device and the blue LED device are installed parallel to each other and fixed to the top of a police car through the alarm lamp leg. The mounting assembly includes a nut and a bolt for fixing the alarm lamp leg to the top of the police car, and a reinforcing plate installed onto an inner side of a police car rooftop for reinforcing the fixation of the alarm lamp leg. The red LED device emits light with a first lighting frequency and the blue LED device emits light with a second lighting frequency. This invention can improve the warning effect of the LED alarm lamp.