A new method has been developed which is suitable for calculating the electrical potential of a point emission source including space charge effects. The method is based on the surface charge method

in which the space charge effects have been considered. A simplification against the structure of point source has been made. In order to avoid the time-consuming computation in the surface charge method

a hybrid method

called "Surface Charge-finite difference" method

has been presented as a supplement. The comparison of numerical and analytical solutions concerning a spherical capacitor has been given in the paper. The method has been applied to calculate the emission feature of a liquid metal ion source. It has been shown that the method is superior to the previous methods in saving the computer time and computer memory and in calculation accuracy.