The study is to add a special optical lens on a photoplethsymography probe, so light source can inject light obliquely on a sensor. By this lens, the probe can consume less energy to achieve the same effect as a normal probe. We use the freeform surface method to design the lens’ radius of curvature, and use optical design software to design a total internal reflection lens and a dioptric lens. The simulation results show that the lens can collect divergent ray emitted by LED, and enhance the optical efficiency by 23%.