The invention discloses a determination method of a fluid volume in vivo based on an ion induction principle and a measuring instrument of a fluid volume in vivo. The determination method consists of a charged ion partition arrangement analysis model and a multi-frequency fitting separation model, the matched measuring instrument consists of an acquisition sensor, a communication circuit, a processing core MCU (Micro Controller Unit) and a battery for power supply. The determination method and the measuring instrument disclosed by the invention can quickly analyze the fluid volume in vivo of an organism in real time, the ion induction charge which is obviously related to the total amount of the fluid volume in vivo can be measured through a non-contacting and purely physical mode so as to conclude the liquid volume in vivo. Through the measuring instrument, the collaborative analysis can be performed on the obtained inductive charge value and the frequency rate of the rise of temperature and humidity, the breathability, water absorption and the like of a hygroscopic nursing material can be evaluated and the comfortable situation is monitored. In addition, the measuring instrument also comprises a mobile terminal and a remote server software system, the remote control can be performed on the measuring instrument at the mobile terminal after the communication circuit is connected with the measuring instrument, and the uploaded data can be further analyzed, stored, managed and visualized.