  Dense gas is the key for understanding star formation in galaxies. We present
high resolution ($\sim3''$) observations of CN 2-1 and CS 5-4 as dense gas
tracers toward Arp 299, a mid stage major merger of galaxies, with the
Submillimeter Array (SMA). The spatial distribution of CN 2-1 and CS 5-4 are
generally consistent with each other, as well as HCN 1-0 in literature.
However, different line ratios of CS 5-4 and CN 2-1 are found in A, B, and C
regions, with highest value in B. Dense gas fraction decreases from IC 694 (A),
to NGC 3690 (B) and the overlap starburst region (C and C$'$), which indicates
that circum-nuclear upcoming starburst in A and B will be more efficient than
that in the overlap region of Arp 299.
