We present the theoretical results of a piecewise isothermal shock wind model. This was devised to predict the luminosity and surface brightness profile of diffuse X‐ray emissions, primarily from the inner shocked downstream wind zone of a planetary nebula (PN) surrounded by a self‐similar shocked dense shell and self‐similar outer slow asymptotic giant branch wind envelope, both involving self‐gravity. We compare and fit our computational model results with the available observations of a few grossly spherical X‐ray emitting PNe. By matching the shocked piecewise isothermal self‐similar void solutions with the self‐gravity of Lou and Zhai for the outer zone and a stationary isothermal fast tenuous wind with a reverse shock for the inner zone across an expanding contact discontinuity, we can consistently construct dynamic evolution models of PNe with diffuse X‐ray emissions. On the basis of such a chosen dynamic wind interaction model, both the X‐ray luminosity and the radial X‐ray brightness profile are determined by three key parameters: the so‐called X‐ray parameter, X, and two radii, Rrs and Rc, of the reverse shock and the contact discontinuity. We find that the morphologies of X‐ray emissions appear in the forms of either a central luminous sphere or a bright ring embedded within optically bright shells. In contrast to previous adiabatic models, the X‐ray brightness peaks around the reverse shock, instead of the contact discontinuity surface just inside the outer shocked dense shell. The diffuse X‐ray emissions of a few observed PNe appear to support this piecewise isothermal wind–wind dynamic interaction scenario with shocks.