The invention provides a low current grounding single phase earth fault diagnosis method, comprising: capturing A voltage to ground, B voltage to ground, C voltage to ground, neutral point current and entire waveform information of each zero sequence current from a steady state to a transient state then to steady state when neutral point voltage exceeds presupposed threshold; first diagnosing whether being single phase earth fault, PT fusing, ferro resonance, arc suppressing coil resonance overvoltage, or neutral point overvoltage disturbance caused by experiment; selecting lines for the earth fault. The inventive method makes full use of steady state information and transient information of electric network before and after fault, and judges the fault and selects lines according to the long term changing rule of the neutral point voltage, which is different from the traditional stable state line selecting method and the transient line selecting method, thereby being suitable for the neutral point unearth electric network and the neutral point arc suppressing coil earth electric network at the same time, and well adapts the condition of complex site, thereby ensuring fault diagnosis and correct line selection.