Abstract: In order to reach demands of tunable lasers in the current optical fiber communication systems, a design concept for wavelength tunable lasers was proposed based on vernier effect. A three-section slotted Fabry-Perot tunable semiconductor laser with stable power and adjustable frequency was designed and its design principle of system structure was given. After theoretical analysis and experimental verification, the lasing spectrum overlay data of the three-section slotted Fabry-Perot tunable semiconductor laser was obtained. Its laser line width was measured by using fiber delay self-heterodyne method. Measurement curves of line widths of three different lasers were compared. The results show that the slotted Fabry-Perot tunable semiconductor laser based on vernier effect is simple and convenient. It has good single-mode performance and channel switching capability. In the future, it has some value and practical significance in the field of optical communication.