A self-optimizing cumulative inversion for particle size distribution with photon correlation spectroscopy is proposed.It improves precision and stability of measurement.From a detailed fundamental of photon correlation spectroscopy and conventional cumulative inversion,we analyze instability of cumulative inversion.A self-optimizing method is presented by using the minimum mean-square error.It inverts particle size distribution stably with scattered autocorrelation curve with random noise.Experimental results illustrate validity and feasibility of the approach.