The complex degree of self-coherence is introduced to quantify the coherence of supercontinuum generated by the same long pulse, and experiments are performed. The coherence properties of supercontinuum generated in the photonic crystal fiber pumped by 700 ps pulse are measured using the Mach-Zehnder interferometer. The experimental results show that the coherence lengths of different wavelength parts of the supercontinuum are all longer than 40 m, and can reach 225 m in the long wavelength region. The coherence degrees of different parts of supercontinuum are not the same; however, the mean coherence degree over the supercontinuum is 0.461 which manifests good coherence property of the whole spectrum of supercontinuum. Consequently, requirements of many applications such as optical measurement and optical sensing can be satisfied.