The Howland current source(HCS)circuit is commonly used,e.g.in electrical impedance tomography(EIT)systems.It is important to optimise the design parameters,such as the output impedance,bandwidth,current stability and load range.While many people have used this circuit,it has not been systematically analysed.In this paper,a numerical method is proposed to analyse the characteristics of HCS.Based on a non-ideal op-amp model,general formulas and simplified formulas for calculating the output impedance and the close-loop gain of HCS are deduced.From these formulas,the practical formulas are chosen and their effectiveness has been proven by analysis and experiment.The output impendence of two HCS circuits based on μA741 and LM6365 are compared.The magnitude-frequency response and the relationship between the current and the load of HCS are discussed. The Howland current source (HCS) circuit is commonly used, egin electrical impedance tomography (EIT) systems. It is important to optimize the design parameters, such as the output impedance, bandwidth, current stability and load range. Whilst many people have used this circuit, it has not been systematically analyzed. This paper, a numerical method is proposed to analyze the characteristics of HCS.Based on a non-ideal op-amp model, general formulas and simplified formulas for calculating the output impedance and the close -loop gain of HCS are deduced. These formulas, the practical formulas are chosen and their effectiveness has been proven by analysis and experiment. The output impendence of two HCS circuits based on μA741 and LM6365 are compared. magnitude-frequency response and the relationship between the current and the load of HCS are discussed.