The pulsed inductive thruster accelerates the propellant by the repulsion between inductive coil and current sheet. To accurately investigate the acceleration characteristics in the first half period of pulsed inductive discharge and the energy needed to generate effective impulse, an unsteady magnetohydrodynamics model is developed, in which the coil-plasma boundary condition is improved by plasma electrical model, and the electrical conductivity is calculated using gas kinetic method. The analysis of plasma electrical characteristics shows confining of particles in the beginning and acceleration of the current sheet after ionization process is completed, leaving behind the low-density residual plasma, with negligible contribution to the total impulse. The impulse at high voltage decreases monotonically after peak value is reached, showing effective impulse generation in the first half period, especially before the decoupling distance is reached.