Small angle X-ray scattering technique was used to study the particle size of precipitated phase of Cu-0.69Cr-0.13Zr alloy aged at 470 °C, and the aging time was from 1.5 h to 3.5 h. The statistical particle size of precipitated phase is 4.97~5.48 nm, and with the aging time increasing, the precipitated phase particles have no obvious growth. When the aging temperature is 470 °C, and the time is 2.5 h, the particle size of the precipitated phase in the sample is about 5 nm measured by the method of transmission electron microscope. The two methods agree well with each other. It shows that the small angle X-ray scattering technique can be used for measuring the size of aging precipitation of Cu-0.69Cr-0.13Zr alloy and the experimental result is accurate. Compared with the transmission electron microscope measurement, the small angle X-ray scattering technique is of more statistical significance and more valuable.