The temperature dependence of the critical current determined by S/N/S junctions is calculated and compared to experimental data in YBa2Cu3O7-x specimens. A quasi-two-dimensional S/N/S junction model is used to simulate the temperature dependence of Jc in the YBa2Cu3O7-x system. Our calculated results fit the experimental data well both in films and in bulk materials, indicating that the critical current is determined by S/N/S junctions, rather than by flux pinning strength.