High-energy-synthesized laser pulses through a nonlinear frequency-conversion process with different characteristics, such as polarization, central wavelength, and pulse duration, play important roles in materials science, high-energy physics, and ultrafast optics. In this study, we present an improved transient-grating frequency-resolved optical gating based on a self-referenced and reflective structure, which enables the single-shot complete measurement of complex high-power synthesized laser pulses in the broadband range and analysis of the nonlinear frequency-conversion process of ultrashort pulses. The waveform/spectrum evolution of both the fundamental and second harmonic pulses in a nonlinear frequency-conversion process with different injected energies was studied for the first time using this method. Moreover, the method was numerically and experimentally verified to be able to completely characterize double pulses with spectral and temporal separation, including the relative phase between the two components. This method has considerable potential for studying the complex physical processes of high-power synthesized laser fields.