Optical analysis is critical to the evaluation of a light-emitting diode (LED) street lamp, especially when the lamp is still in its early stage of development and applications and when optimization is needed for making use of unique characteristics of LEDs. In this study, optical analysis of an 80-W LED street lamp was conducted. Experimental research on such a lamp was first undertaken. The results demonstrated that the average illumination was about 8.25 lx and the total uniformity was 0.364 for a 20-m-long and 10-m-wide test area at a height of 8 m, which is acceptable for the current standard for a submain road. Numerical simulation was also conducted; the feasibility of the numerical model was proven by comparison of the simulations with the experimental data, which will be used for future optimization study and other novel designs of the optical system of street lamps. Through the simulations and the corresponding analysis, it was found that the tested 80-W LED street lamp had reasonable performance in average illumination, but multiple shadows existed, which would need to be removed in future designs. Improvements are suggested to reduce the number of optical elements, to reduce the lamp's volume, and to enhance the illumination performance. Two design methods for LED street lamps are summarized, based on the optical analysis.