The Xpendable Current Profiler (XCP) probe is the latest jettison marine probe, which has an important strategic significance in the ocen exploration, sinitific research, and military. The attitude of the XCP probe in the seawater directly affects the precision of current measurement. The experimental research on the underwater attitude of the probe is important to the development of expendable current measurement technology. The two-dimensional instantaneous and time-averaged flow fields for the horizontal section of XCP probe are measured using Time Resolution Particle Image Velocimetry (TRPIV) technology, through test device built in the interior experimental channel. The influence of rotating speed rate and Reynolds number on the flow field is analyzed, and the side force is obtained according to Magnus effect. The study results show that the side force is proportional to the rotating speed rate, and increases as the Reynolds number increasing. Based on the analysis, when the probe is in the state of whereabouts, the side forces change. Therefore, the probe is actually in the declining state. The results could provide the reference and basis for estimating the declination solution of the probe.