The invention discloses a device for reinforcing a foundation through microbial ultrasonic grouting and a construction method thereof. The device comprises a grouting pipe, the upper side of the grouting pipe is connected with an ultrasonic energy concentrator, the ultrasonic energy concentrator comprises an ultrasonic amplitude transformer and an ultrasonic transducer, the ultrasonic transducer is connected with the upper end of the ultrasonic amplitude transformer and the upper end of the grouting pipe, a pulse generator is arranged at the bottom of a grouting hole, an ultrasonic sensor is arranged on the ground on one side of the grouting pipe, the ultrasonic sensor is connected with an oscilloscope, the upper end of the grouting pipe is connected with a grout inlet pipe, the grout inlet pipe is connected with two grout inlet barrels through a grouting pump, and the two grout inlet barrels are filled with bacterial liquid and cementation solution respectively. According to the device, the reinforcement uniformity can be improved, deeper soil bodies can be reinforced, grout can be diffused to the periphery from the grouting pipe with holes in the pipe wall in cooperation with the ultrasonic effect, the reinforcement range is larger, the integrity is higher, the reinforcement uniformity is guaranteed, and the applicable soil body types are wide.