The emission spectrum of light emitting diode (LED) are calculated by using the LED spectral model of Ohno, and then the spectral combination of multi-LEDs has been investigated theoretically and experimentally. In the experiment, the warm white light, which is obtained by blue LED die exciting green and orange phosphor, and red, cyan, blue LED light are mixed. By respectively controlling the duty ratio of the pulse width modulation (PWM) signals, the drive currents and luminous flux of each LED can be adjusted. A mixed white light source with ultra-high color rendering index has been realized for the first time, whose color temperature can be tunable within the range of 2700 K to 6500 K, Ra is between 95 to 98, all special CRIs (R1~R15) are more than 90, and luminous efficiency of radiation (LER) is between 286 lm/W to 336 lm/W .The consistency of experimental measurements and theoretical simulation are very well.