The present study has numerically simulated the oxy-fuel combustion of a methane (CH4) jet in hot coflow (JHC). The main objective is to investigate the influences of the oxygen (O-2) molar fraction (X-O2*), temperature (T-cof*) and velocity (v(cof)*) of the O-2/CO2 coflow on dimensions of the JHC reaction zone or flame. The simulations use the model of eddy dissipation concept (EDC) with the detailed chemical mechanism described by GRI-Mech 3.0. To validate the modeling, several air-fuel JHC flames are predicted under the same conditions of the work of Daily et al. [Proc. Combust. Inst. 2002, 29, 1147-1154]; the predictions match well with the measurements. Results suggest that, as either X-O2* or v(cof)* decrease or T-cof* increases, the volume of the JHC reaction zone increases and hence the overall oxidation rate of CH4 decreases. In particular, raising the coflow speed v(cof)* causes the flame to be significantly thinner but only slightly longer. It is also demonstrated that the oxy-fuel reaction zone is larger, and so, the temperature is lower than the air-fuel counterpart. Besides, under identical conditions, the oxy-fuel combustion produces more carbon monoxide than does the air-fuel combustion.