Abstract: The behavior of three-dimensional turbulent boundary layer in the attached flow region induced by a straight wing erected on a flat plate at low and subsonic speeds has been determined experimentally .The effects of pressure gradient and streamline curvature on the distributions of mean velocity and turbulent values are discussed in this paper.The experimental study reveals the followings:（1） Application of the wall and wake law suitable for two-dimensional turbulent boundary layer to describing the mean velocity distribution in the three-dimensional case is reasonable on condition that the pressure gradient and the streamline curvature are mild, and the coefficients in the wall/wake law expression should be varied according to the pressure gradient and the streamline curvature. （ 2 ） Peaks are found in the distributions of turbulent values and turbulent stresses.They appear to move away from the wall with the increase of the adverse pressure gradient and to flatten with the increase of the streamline curvature. （ 3 ） The mixing length distribution does not keep invariant, as the slope of its straight part in the inner part decreases with the increase of the pressure gradient and its maximum value increases with the increase of the streamline curvature. （ 4 ）The behavior of the three-dimensional turbulent boundary layer at subsonic speeds is qualitatively similar to that in the low speed case.But this problem deserves further investigation.