A geometry of transient-grating self-referenced spectral interferometry (TG-SRSI) is proposed for weak femtosecond pulse characterization. By using a reflective microscope objective (RMO), we build a compact, robust, and easy to adjust device with a higher sensitivity to pulse energy in comparison to all previous SRSI methods. A 65 nJ/～40 fs/1 kHz pulse at 800 nm is successfully characterized, which speaks to the capability of our device to characterize a weak pulse. It is expected to extend the TG-SRSI method to the characterization of femtosecond pulses from oscillators in the near future.