The isolated tissue samples are illuminated by using the LED radiation sources at different wavelengths. Then, the ray transmitted through the tissue samples is received by using a spectrometer. The waveform and wavelength distribution of the ray transmitted through the tissue samples from the LEDs are compared. The frequency spectra of the ray transmitted through the same tissues at different frequencies is analyzed. Finally, the optimal wavelength range for the LEDs to transmit the tissues is obtained. This result is instructive to the application of the LED radiation sources to therapy products.