Did you check the relation of each line to verify that one is vertical and the other is horizontal? Also posting your model would help immensely.
Tran Van Quang wrote:
I draw a vertical line in a sketch, then I draw a horizontal line in another sketch. The problem is the angle between them only 89.87 degree not 90 degree as I expected. May anyone know ho to solve it. Thank you
You state that you used two sketches.
Dpending on the relative position between the two sketch planes, you may not get 90° between them even if they're horizontal and vertical in their own sketches,
Orientation is dictated within each sketch plane.
There are methods to make the horizontal line in the second sketch to be perpendicular to the line in the first sketch, but making it horizontal using a relation isn't a guarantee.
But as Solid Air posted, please upload your part if possible or least provide some screen shots (including the feature tree) so we can provide better replies instead of guesses.