The invention discloses a laser capable of monitoring cutting state in real time. A laser gain medium fiber core is wrapped by a glass isolation layer, a fluorescent material layer and an external wrapping layer from the inside out in sequence; the refractive index of the laser gain medium fiber core is larger than that of the glass isolation layer; the refractive index of the glass isolation layer is larger than that of the fluorescent material layer; and the refractive index of the fluorescent material layer is larger than that of the external wrapping layer. The input end and the output end of a clad fiber are provided with a first fiber Bragg grating and a second fiber Bragg grating respectively. The end surface, arranged at the side of a pump light source, of the clad fiber is provided with a tail mirror. A first convex lens and a second convex lens are sequentially arranged between the clad fiber and a transmission fiber. A semi-reflection semi-permeable wafer is arranged between the first convex lens and the second convex lens; and the semi-reflection semi-permeable wafer and the light path are arranged in a manner that an acute angle is formed therebetween. When the cutter cuts a high-reflecting material, that laser wavelength surpasses a set threshold value can be detected in real time, so that the cutter can stop quickly to prevent the laser from returning in the original path; and response time is short due to light speed.