Abstract: Astronomical spectroscopy is a critical tool in many advanced research topics such as cosmic origin, galaxy evolution, stellar formation, and exoplanet detection. Medium-to-large aperture optical telescopes equipped with various spectrographs are suitable for many large programs. However, many small-aperture (30–80 cm) telescopes have the potential to perform quick and flexible observations in the astronomical field. Using current technology, most portable astronomical spectrographs can capture broadband spectra by rotating or changing the gratings to scan the spectrum at multiple exposures. This paper presents a portable broadband astronomical spectrograph (called ESPEC-2) that features an echelle grating as the main disperser and a group of collimating and imaging lenses to simplify the optical system. For 30–80 cm aperture telescopes, the lightweight prototype (~3.5 kg) enables spectral observation with a spectral resolution of R ≥ 6200 over a wavelength range of 400–900 nm with a single exposure. Moreover, it can be directly mounted on the telescope’s focus or connected via optical fiber. Its portability and versatility make it suitable for use as a general-purpose spectrograph in other scientific experiments. The developed compact broadband spectrograph is expected to make significant contributions to scientific research, outreach, and education.