The effect of source size and emission time on the proton–proton (p–p) momentum correlation function (Cpp(q)) has been studied systematically. Assuming a spherical Gaussian source with space and time profile according to the function S(r, t)～exp(-r2/2r20-t/τ) in the correlation function calculation code (CRAB), the results indicate that one Cpp(q) distribution corresponds to a unique combination of source size r0 and emission timeτ. Considering the possible nuclear deformation from a spherical nucleus, an ellipsoidal Gaussian source charac-terized by the deformation parameter ∈=ΔR/R has been simulated. There is almost no difference of Cpp(q) between the results of spherically and ellipsoidally shaped sources with small deformation. These results indicate that a unique source size r0 and emission time could be extracted from the p–p momentum correlation function, which isespecially important for identifying the mechanism of two-proton emission from proton-rich nuclei. Furthermore, considering the possible existence of cluster structures within a nucleus, the double Gaussian source is assumed. The results show that the p–p momentum correlation function for a source with or without cluster structures has large systematical differences with the variance of r0 andτ. This may provide a possible method for experimentally observing the cluster structures in proton-rich nuclei.