The invention discloses a waste water online biological monitoring method and a waste water online biological monitoring device, and belongs to the field of waste water online monitoring. The device consists of a 
circulating pump (3), a 
liquid storage chamber (2), a circulation chamber (1), an inductive 
electrode (4) and a 
multimeter (5); the 
circulating pump is arranged at the lateral bottom of the 
liquid storage chamber away from the circulation chamber, and is connected with the circulation chamber via a plastic 
pipe; the sidewall of the circulation chamber is connected with side surface of the 
liquid storage chamber at the equal height to realize flow 
exposure of the whole course. Two pairs of 
copper electrodes with nuts are arranged on the inner side of the circulation chamber, wherein one pair of the electrodes functions as an input end of an electrical 
signal, and the other pair of the electrodes is connected with the 
multimeter to form an output end of the electrical 
signal. The distribution of an 
electric field in the circulation chamber can be influenced by swimming of the tested 
organism daphnia, namely the change of output current or 
voltage. By the invention, whether the quality of the discharged water is safe can be intuitively reflected; meanwhile, an 'electronic eye' is provided for the 
pollution incident monitoring and the dispute resolution monitoring of an 
environmental monitoring department. The device disclosed by the invention is simple in structure and strong in mobility and can be used indoors and outdoors.