A multifunctional rearview mirror includes a casing having first and second receiving spaces. A mirror is mounted to one side of the casing that is formed with the first receiving space. The second receiving space is located under the first receiving space and has a front surface formed with first through-holes. A distance detection and alarm unit is arranged in the second receiving space and includes an ultrasonic distance detection module, an alarm light module, and a buzzer. The ultrasonic distance detection module is eclectically connected with the alarm light module and the buzzer. The alarm light module is arranged in the first through-holes. The ultrasonic distance detection module emits an ultrasonic wave, which is returned to the ultrasonic distance detection module by an object, so that a distance to the object is calculated and the alarm light module and the buzzer are activated according to the distance.