  In the quantum chromodynamics, the mass source of the proton is decomposed
into four parts by the energy momentum tensor : quark energy term, gluon energy
term, quark mass term and trace anomaly term. And the trace anomaly term is the
most crucial contribution for studying the internal structure of the proton. In
this work, under the definition of the vector meson dominant model, the trace
anomaly contribution of the proton is extracted from the experimental datas of
light vector mesons $\rho$, $\omega$ and $\phi$ photoproduction at the
near-threshold, which are ($1.15\pm0.08$)$\%$, ($2.70\pm0.04$)$\%$ and
($5.58\pm0.25$)$\%$, respectively. Eventually, the average trace anomaly
contribution of the proton is ($4.36\pm0.40$) $\%$, which only account for a
small fraction of the total proton mass. The result of this work will provide
theoretical information support for further study of proton internal structure.
