To reduce the calibration uncertainty of spectral radiance responsivity, a new tunable laser-based integrating sphere source was developed. In this facility, high-power, tunable laser outputs were introduced into an integrating shpere, producing uniform, quasi-Lambertian, high radiant flux planar source. Ti:sapphire laser 710 nm output light was used to study the radiometric characteristics of the source. While two-beam paths were introduced into the sphere and laser speckle was eliminated, the radiance instability was 0.06% in 30 min; the radiance was spatially uniform within 0.16% over the most central region 60 of the sphere exit port; the angular nonuniformities in horizontal and vertical plane within the range of ±22° were 1.3% and 0.7% respectively. This source have the advantages of high stability, high spectral radiant flux, narrow bandpass, large area, tunable wavelength in broad spectral range, etc. The radiometric properties of the source couple with state-of-the-art standard detector whose responsiveness are directly traceable to primary radiometric scales can reduce the calibration uncertainty effectively.