The current-voltage characteristics of Ag-sheathed Bi-2223 tape for high-temperature superconducting coils are measured as a function of the magnetic field and its flux angle to the tape at liquid nitrogen temperature. The approximate characteristic equations on critical currents and n values are obtained from this result. Then, the electric field distribution inside the coil can be calculated with the approximate characteristic equations. The current-voltage characteristics of high-temperature superconducting coil are analyzed and compared with the test result of conduction-cooled coil, producing relatively good agreements. The coil performances can be made clearer with the assistance of characteristic equations at the coil design stage and, further, the optimum coil design will be made possible. (C) 2002 Elsevier Science B.V. All rights reserved.