  Noise is a significant part within a millimeter-wave molecular line datacube.
Analyzing the noise improves our understanding of noise characteristics, and
further contributes to scientific discoveries. We measure the noise level of a
single datacube from MWISP and perform statistical analyses. We identified
major factors which increase the noise level of a single datacube, including
bad channels, edge effects, baseline distortion and line contamination.
Cleaning algorithms are applied to remove or reduce these noise components. As
a result, we obtained the cleaned datacube in which noise follows a positively
skewed normal distribution. We further analyzed the noise structure
distribution of a 3D mosaicked datacube in the range l = 40{\deg}.7 to
43{\deg}.3 and b = -2{\deg}.3 to 0{\deg}.3 and found that noise in the final
mosaicked datacube is mainly characterized by noise fluctuation among the
cells.
