The transverse-momentum-dependent (TMD) soft function is a key ingredient in QCD factorization of
Drell-Yan and other processes with relatively small transverse momentum.
We present a lattice QCD study of this function at moderately large rapidity
on a 2+1 flavor CLS dynamic ensemble with $a=0.098$ fm. We extract the rapidity-independent (or intrinsic) part of the
soft function through a large-momentum-transfer pseudo-scalar
meson form factor and its quasi-TMD wave function using leading-order factorization
in large-momentum effective theory.
We also investigate the rapidity-dependent part of the soft function---the Collins-Soper evolution kernel---based on the large-momentum evolution of the quasi-TMD wave function.