  Precise cosmological measurements are essential for understanding the
evolution of the universe and the nature of dark energy. The Five-hundred-meter
Aperture Spherical Telescope (FAST), the most sensitive single-dish radio
telescope, has the potential to provide the precise cosmological measurements
through neutral hydrogen 21-cm intensity mapping sky survey. This paper
primarily explores the potential of technological upgrades for FAST in
cosmology. The most crucial upgrade begins with equipping FAST with a wide-band
receiver ($0 < z < 2.5$). This upgrade can enable FAST to achieve higher
precision in cosmological parameter estimation than the Square Kilometre Array
Phase-1 Mid frequency. On this basis, expanding to a FAST array (FASTA)
consisting of six identical FAST would offer significant improvements in
precision compared to FAST. Additionally, compared with the current results
from the data combination of cosmic microwave background, baryon acoustic
oscillations (optical galaxy surveys), and type Ia supernovae, FASTA can
provide comparable constraints. Specifically, for the dark-energy
equation-of-state parameters, FASTA can achieve $\sigma(w_0) = 0.09$ and
$\sigma(w_a) = 0.33$.
