The collimation system of reducing smoke alarm system collects wide angle near infrared rays to generate the parallel beam, which ensures that the rays travel long distances without divergence. Reducing smoke alarm collimation system is optimized by point by point calculation. The initial discrete data points of smoke alarm system for ideal point light source are calculated based on the principle of equal optical path and refraction law. The discrete data points are fitted into freeform curves. Using optical simulation software to build the model and optimize the initial structure of the collimation system, and better LED freeform collimation system is got. The thickness of freeform surface collimation system is 20 mm, the diameter is 28 mm, the collimation angle is ±1.5° and the energy efficiency is 89.82%.