The correlations for cross-flow have not been well established, because of the complexity of breakup and atomization mechanism. A study was performed to investigate the characteristics of spray behaviour of liquid jet in the bag breakup regime injected into low-speed cross-flow with the pressure single-hole nozzle. The shadow-graphy method was used for the cross-flow jet visualization. The experimental variables of liquid jet were nozzle diameter $(0.3mm{sim}1.0mm)$, injection pressure $(50kPa{sim}150kPa)$, and the velocity of cross-flow $(27m/s{sim}42m/s)$. The highest penetration trajectories of liquid jet are governed by the momentum ratio $({ ho}_{iota}U_{iota}^2/{ ho}_aU_{cross}^2)$ rather than the Weber number and the new empirical equations of the highest penetration trajectory and breakup point at low-speed corss-flow are established.