The invention discloses a real-time distance measuring device, system and method for high-grade leveling, and belongs to the field of horizontal distance measurement. In order to solve the problems that in the prior art, the sight distance error is large before and after level gauge measurement, the consumed time of a distance measuring instrument is long, and power consumption is high, the invention provides a real-time distance measuring device, system and method for high-grade leveling; the device comprises an upper shell and a lower shell, circuit boards are arranged in the upper shell andthe lower shell, and antennas are installed on the circuit boards; each circuit board further comprises a man-machine module, a control module, a sensing module, a monitoring module and a power supply module, when the device measures the distance, the antenna with the optimal signal is calculated through an antenna switching algorithm, the long distance measuring time due to bad single antenna signal is avoided, the distance measuring result can be obtained more accurately and rapidly, meanwhile, the power consumption of the device is reduced, and installation is convenient; and the device can be installed on a level gauge for common movement.