The invention discloses a method for dynamically measuring width of a steel billet by using laser displacement sensors. The method includes that 1, two laser displacement sensors are mounted on two sides of a roller way respectively before the steel billet is swept, and a camera is adopted to photograph the steel billet currently moving on the roller way; 2, an industrial control computer sequentially calculates discrete width value of the current steel billet and correspondingly displays matched width curve, discrete width value and video images capable of showing the surface of the steel billet currently moving on the roller way in real time through a display screen; 3, the industrial control computer compares planed steel billet width with the discrete width value acquired by calculating the steel billet currently moving on the roller way; when width difference value acquired through subtraction of the planned steel billet width and the discrete width value exceeds a set difference value range, an optical triangular measuring device is allowed to give out sound for alarming, the discrete width value Width is enabled to be in one-to-one correspondence to corresponding billet number, planned steel billet width and mark digit to form relevant data, and the relevant data formed correspondingly in real time are stored. By the method, measuring technical means is simplified, and requirements on accuracy in actual measuring of steel billet width are met.