The invention discloses an assembly method for guide vane assemblies, and belongs to the field of machining and manufacturing of guide vanes of aero-engines. The method includes the steps of machining vane bodies; fixing the vane bodies to a clamp; measuring feature points of profiles of installation heads of the vane bodies; machining first installation plates and second installation plates; polishing first profile holes of the first installation plates and second profile holes of the second installation plates; fixing the polished first installation plates to the clamp; carrying out trial assembly on the first installation plates and the vane bodies; fixing the polished second installation plates to the clamp; carrying out trial assembly on the second installation plates and the vane bodies; carrying out infirm spot welding locating on the first installation heads of the vane bodies and the first profile holes; carrying out infirm spot welding locating on the second installation heads and the second profile holes; and measuring exhaust areas of throats of the preassembled guide vane assemblies and rotating the multiple vane bodies until design requirements are met if the exhaust areas are smaller than areas of the design requirements. According to the method, the polishing and modifying positions can be judged fast and accurately, and the areas of the throats can be adjusted fast.