The invention discloses a device for online measuring dynamic performance of an ultra-precision hydrostatic spindle and a method for measuring the dynamic performance of the hydrostatic spindle by using the same, and relates to the method for online measuring the dynamic performance of the ultra-precision hydrostatic spindle. The problem that in the convention method, online measurement of the dynamic performance of the ultra-precision hydrostatic spindle cannot be carried out, or influence of an installing error and a manufacturing error of a measuring benchmark on a measuring result is difficultly avoided is solved. The method provided by the invention comprises the following steps: acquiring displacement information between a sensor and a standard ball by using a high-precision displacement sensor; amplifying the acquired displacement information by a signal amplifier; inputting the acquired displacement information into a computer after passing through an A/D (analog/digital) conversion circuit and a data acquisition circuit; acquiring phase information of the spindle and inputting the phase information into the computer by using a rotary encoder; analyzing and processing the phase information by the computer to obtain error data of the rotating dynamic performance of the ultra-precision hydrostatic spindle, thereof implementing the online measurement of the dynamic performance of the ultra-precision hydrostatic spindle. The device and the method are applicable to the online measurement of the dynamic performance of the ultra-precision hydrostatic spindle.