Abstract: We proposed a high-efficient method for the design of the LED lens generating the required irradiance distribution in a rectangular area with a large aspect ratio which was named division-design method:the part of total-internal-reflection(TIR) was designed based on Snell’s law and edge-ray principle,and calculated by iterative integral method,besides,the Matlab programming method was used for its 2D contour;the part of transmission was designed based on the trial and error method; then the two parts were integrated together into a novel arch lens by SolidWorks with the size of 25 mm×18 mm×10 mm. The simulation and experiment results show that the efficiency of the light system is up to 85% while the lens matches with the LED extended source, and the beam angle is about 9°×135° wide at the position of halfvalue of the peak light intensity which means generating the uniform irradiance distribution in a rectangular area with an aspect ratio larger than 15 .