The invention relates to a constant current module for an excitation signal transmitting system of a mineral electrical prospecting apparatus. The constant current module consists of an input level, an output level and a feedback control level, wherein the input level inputs underground AC (Alternating Current), and high precision constant current output is obtained by passing through EMI-RFI (Electro-Magnetic Interference-Radio Frequency Interference) filter and rectifier filter, and then passing through a high frequency transformer and rectifier filter of the output level; voltage sampling and current sampling are carried out before the output, a voltage sampling signal is compared with reference voltage after the voltage sampling signal is amplified by a voltage error, a current sampling signal is compared with a constant current control signal after the current sampling signal is amplified by a current error, and then the two sampling signals are input to an optocoupler as feedback signals, and a power switch device is controlled to feed back the two signals to the input level through the optocoupler. According to the feedback signals obtained by the feedback, a processing circuit of the input level carries out corresponding adjustment to obtain stable constant current output; furthermore, the constant current module is applicable to various excitation signal transmitting systems of the mineral electrical prospecting apparatus, and the constant current output current with high precision can be provided.