Why is the radiation pattern not oriented to the 0 degree? I got this raditaion pattern after simulation, but I wonder to know that why is the radiation pattern not oriented to the 0 degree instead of 90 dgree?
Your antenna has main beam at theta=90° and phi=0°, that is in the xy plane (PCB plane) and not upwards in z direction. No problem with that, if you show the antenna and related xyz coordinate system.
If you insist to "fix" this and get main beam at theta=0°: You could rotate the complete model so that the antenna radiates to z axis, but there might be easier solutions. My EM solver (Empire XPU) has a feature to rotate antenna patterns in postprocessing, maybe HFSS has a similar feature.