A temporal signal measurement equipment for current 100 Gb/s fiber optic transmission, based on the linear optical sampling technique, is proposed and experimentally demonstrated. In the self-developed prototype, a passively mode-locked fiber laser is used as optical sampling source with a pulsewidth of 2 ps and repetition frequency of 96.25 MHz. Then, the polarization division multiplexing quadrature phaseshift keying (PDM-QPSK) signal under test is optically mixed with the sampling pulse before phase and polarization diversity detection. With the help of four-channel 400 MHz balanced photodetectors, four-channel analog signals are transmitted to the mainframe, for the purpose of digital signal processing and result display. By optimizing the design, pulse power, central wavelength, repetition frequency of passively mode-locked fiber laser can be output stably. Furthermore, the performance comparison with the counterpart from Agilent modulation format analyzer (N4391A) is carried out, and it’s verified that the prototype has almost the same capability for on-site measurement.