The effects of magnetic field on the free surface flow around a cylinder were investigated experimentally using the PIV(particle image velocimetry) under Reynolds number 7767 and 11650.The experimental result revealed that the field enabled the distribution of nondimensional average velocity to deviate from logarithmic distribution of nondimensional average velocity in the boundary layer

and also made the wake become narrower and shorter

and the detachment point move backward.When the Reynolds's number reached up to 11650

the influence of magnetic field was weaken under same strength of external magnetic field.Consequently

the departure degree between the nondimensional average velocity distribution and logarithmic distribution in the boundary layer was reduced.