A balloon catheter system assisted by ultrasound and microbubbles and a method for vasodilation are provided. The system includes: a controller; a sensor catheter; a highly focused ultrasound probe, and the highly focused ultrasound probe and the sensor catheter is connected to the controller; and a balloon catheter. The method of vasodilation includes: providing a sensor catheter into a blood vessel, and controlling a highly focused ultrasound probe to focus at a hardened portion of the blood vessel; removing the sensor catheter from the blood vessel and inserting a balloon catheter into the blood vessel; infusing microbubbles into the balloon catheter and controlling the highly focused ultrasound probe to start working to destroy a calcification point of the hardened portion of the blood vessel, and smoothly inflating the balloon catheter at the hardened portion of the blood vessel.