Targeting poor color rendering property of current white light-emitting diode (LED) lamps, based on the colorimetry method, the calculation model for color rendering index of synthetic white light is studied and the parameters like color temperature and color rendering index of the synthetic LED light source are obtained based on the spectrum and quantity of light sources involved in the synthesis process. By using optimized traversal range, the spectra of cold and warm white light and single- color LEDs are imported into the program for simulating calculation, obtaining the maximum value of color rendering index of the synthesized light source under different color temperatures as well as corresponding matched quantity of various LEDs. The results show that the synthesis with warm white LEDs and red, green and blue LEDs can lead to white light whose color temperature falls in the range of 3500 K~12300 K and color rendering index Ra ranges between 92.0 and 97.7. The synthesis with warm white LEDs and red, green and bluish-green LEDs can lead to low color temperature white light (3500 K~4500 K) whose color rendering index R_a ranges between 95.0 and 97.8. The synthesis with cold white LEDs and red, green and bluishgreen LEDs can lead to high color temperature white light (8200 K~13000 K) whose color rendering index R_a ranges between 90.9 and 98.4. An actual fabrication is conducted following the calculated LED amount to produce an LED module with 7803 K color temperature and 97.29 color rendering index. Actual measurement shows that the produced LED module has a color temperature of 7992 K and a color rendering index of 97.1, which is well matched the theoretical results.