Low-coherent light pulses with precise time-shaping capability have the potential to suppress the instability of laser-plasma interactions in laser inertial confinement fusion, but related research is currently lacking. In this paper, the law of the influence of the amplitude modulator on the time-frequency characteristics of broadband low-coherent light was studied, and the intensity of the light pulse was modulated by changing the RF coefficient and bias voltage of the Mach-Zehnder interferometric amplitude modulator. The time domain waveform distribution, spectrum and complex coherence modulus curve of the modulated light pulse were analyzed. The research shows that the RF coefficient has no obvious modulation on the spectral composition and temporal coherence of the light pulse, and the RF coefficient has an optimal working range, which makes the waveform fidelity of the output light pulse the best. When the bias voltage is at half-wave voltage, the time domain waveform fidelity of the optical pulse is the best, and the temporal coherence is the lowest, but the spectral components are missing. The arm length difference of the modulator is calculated from the measured spectrum, and the influence of the arm length difference and bias voltage on the frequency domain characteristics of the broadband low-coherent light is simulated theoretically, the results are in good agreement with the experimental results. As the actual electro-optic overlap integration factor changes with the voltage, there is an error between the simulation and the actual measurement results. However, the laws obtained from the research will provide a more clear direction for low coherent pulse precision shaping system development.