A design of spectral tunable Light Emitting Diode(LED) light source composed of an integrating sphere and a large number of LEDs was described.The source was designed to produce different spectral distributions in the visible region,and it could simulate the spectral distributions for various light sources.A series of simulations were conducted to predict the performance of spectral distribution of the designed tunable source and a power control box in the source was designed to control every LED module accurately.Experimental results show that the uniformity of the source is 0.53%,and the performance of the angle is 0.77% in ±10°.This new type of source can be used as a transfer standard for radiometric application.