The integral expression of magnetic induction distribution by a single current-carrying circular coil at any point is analyzed through Biot-Savart law. The analytical results are obtained and the distribution of magnetic induction lines are described by using Mathematic. The characteristics of magnetic induction distribution on the circular surface，where the current-carrying circular coil is located，are also analyzed. Besides，the magnetic induction distribution of long straight solenoid at any point is discussed by the results of current-carrying circular coil. The“uniform region”of magnetic field distribution is discussed and analyzed by numerical calculation. The distribution of magnetic induction line is described by Mathematica. Finally，the problems related to College Physics and College Physics Experiments are discussed.