A new reflective photoplethysmography (PPG) sensor module is developed with effort to optimize the distances between light emitting diodes (LEDs) and a photodiode (PD) in the proposed module for precision cuffless, non-invasive blood pressure (BP) measurement based on PPG of wrist artery. In the developed module, four LEDs with different wavelengths of 530 nm, 660 nm, 850 nm, 940 nm are included. A new optical simulation model based on Beer-Lambert's law is established, which include LEDs, PD, epidermis, dermis, subcutaneous tissue and pulsating arteries. The distances between LEDs and PD are optimized to maximize the signal-to-noise ratio of the PPG received by PD for higher precision of the predicted BPs from arterial PPG. The results show that the optimal distance is around 2 mm for detecting arterial pulsation by wavelengths of 850 and 950 nm. Experiments were also conducted, showing favorable results of BP measurements.