  The CH$_3$O and CH$_2$OH radicals can be important precursors of complex
organic molecules (COMs) in interstellar dust. The COMs presumably originating
from these radicals were abundantly found in various astronomical objects.
Because each radical leads to different types of COMs, determining the
abundance ratio of CH$_3$O to CH$_2$OH is crucial for a better understanding of
the chemical evolution to various COMs. Recent work suggested that the reaction
between CH$_3$OH and OH on ice dust plays an important role in forming CH$_3$O
and CH$_2$OH radicals. However, quantitative details on the abundance of these
radicals have not been presented to date. Herein, we experimentally determined
the branching ratio (CH$_3$O/CH$_2$OH) resulting from the CH$_3$OH + OH
reaction on the water ice surface at 10 K to be 4.3 $\pm$ 0.6. Furthermore, the
CH$_3$O product in the reaction would participate in subsequent diffusive
reactions even at a temperature as low as 10 K. This fact should provide
critical information for COMs formation models in cold molecular clouds.
