The effect of the interaction between hyperons on the properties of proto neutron star (PNS) PSR J0740+6620 is examined with relativistic mean field theory in consideration of a baryon octet. The nucleon coupling constant GM1 is used and the temperature of the PNS is chosen as T = 20 MeV. Under the constraint of the mass of the PNS PSR J0740+6620 M = 2.14 M $$_{\odot }$$ ${}_{\odot }$ , the PNS’s radius decreases by 0.13% from R = 14.262 km to R = 14.243 km, the central chemical potential of the neutron increases by 0.23% from $$\mu _{n,c}$$ ${\mu }_{n,c}$ = 6.868 fm $$^{-1}$$ ${}^{-1}$ to $$\mu _{n,c}$$ ${\mu }_{n,c}$ = 6.884 fm $$^{-1}$$ ${}^{-1}$ , the central chemical potential of the electron decreases by 1.4% from $$\mu _{e,c}$$ ${\mu }_{e,c}$ = 1.001 fm $$^{-1}$$ ${}^{-1}$ to $$\mu _{e,c}$$ ${\mu }_{e,c}$ = 0.987 fm $$^{-1}$$ ${}^{-1}$ and the central energy density increases by 1.4% from $$\varepsilon _{c}$$ ${\epsilon }_c$ = 1.117 $$\times 10^{15}$$ $\times {10}^{15}$ g cm $$^{-3}$$ ${}^{-3}$ to $$\varepsilon _{c}$$ ${\epsilon }_c$ = 1.133 $$\times 10^{15}$$ $\times {10}^{15}$ g cm $$^{-3}$$ ${}^{-3}$ , taking into account the interaction between the hyperons. The interaction between hyperons also has an effect on the effective mass and the effect is greatest at the centers of PNSs. Baryons n, p, $$\varLambda $$ $\Lambda$ , $$\varSigma ^{+}$$ ${\Sigma }^{+}$ , $$\varSigma ^{0}$$ ${\Sigma }^0$ , $$\varSigma ^{-}$$ ${\Sigma }^{-}$ , $$\varXi ^{0}$$ ${\Xi }^0$ and $$\varXi ^{-}$$ ${\Xi }^{-}$ all will be generated in PNS PSR J0740+6620 regardless of whether the interaction between hyperons is considered. Considering the interaction between hyperons, the relative density of n decreases, while the relative density of p, $$\varLambda $$ $\Lambda$ , $$\varSigma ^{+}$$ ${\Sigma }^{+}$ , $$\varSigma ^{0}$$ ${\Sigma }^0$ , $$\varSigma ^{-}$$ ${\Sigma }^{-}$ , $$\varXi ^{0}$$ ${\Xi }^0$ and $$\varXi ^{-}$$ ${\Xi }^{-}$ increases, indicating that more n are converted into p and hyperons such as $$\varLambda $$ $\Lambda$ , $$\varSigma ^{+}$$ ${\Sigma }^{+}$ , $$\varSigma ^{0}$$ ${\Sigma }^0$ , $$\varSigma ^{-}$$ ${\Sigma }^{-}$ , $$\varXi ^{0}$$ ${\Xi }^0$ and $$\varXi ^{-}$$ ${\Xi }^{-}$ in the PNS.