Orthogonal experiments were carried out for high grade gray water treated by combinational technique of coagulation sedimentation and constructed wetland. With the orthogonal experiment of coagulation sedimentation pretreatment, it is shown that the regression equations relating to effluent BOD5, cubage loads(Nv), temperature(T) and PAC addition dosage(ρ) is BOD5=2.05Nv-0.41T-0.82ρ+38.9. For the orthogonal experiment of constructed wetland posttreatment, it is shown that the regression equations relating to effluent BOD5, cubage loads(NA), and temperature(T) is BOD5=1 190 NA-0.32T+12.2. Based on the two orthogonal regression equations, combined with reclaimed water quantity requirements in different seasons in buildings, an investment optimization model of combinational technique was established. According to the model, the reasonable scale of the reclaimed water treatment systems can be determined and treatment efficacy can be well predicted.