SeaQuest at FNAL is a fixed-target experiment to measure the Drell–Yan process in $p+p$ and $p+A$, using the 120-GeV proton beam and targets of liquid hydrogen, liquid deuterium, carbon, iron and tungsten. SeaQuest aims at precisely measuring the flavor asymmetry of light-antiquark distributions $(\bar{d}(x)/\bar{u}(x))$ at large $x$ in the nucleon. It also measures the angular distribution of the Drell–Yan process in $p+p$ and $p+d$ in order to investigate the Lam–Tung relation and further the Boer–Mulders distribution function. It also utilizes the Drell–Yan process in $p+A$ for measuring nuclear effects, including the nuclear dependence of sea quark distributions and the parton energy loss in cold nuclear matter. Here, the results of $\bar{d}/\bar{u}$ are shown.