Modified Housner model is presented in the paper for seismic analysis of aqueducts on rigid buttress. Invective mass is attached to walls of aqueducts rigidly instead of springs with low stiffness, which ensures vibrating frequencies can be computed. The coefficient α of invective mass is introduced to adjust the enlargement brought by the rigid attachment. The value of the efficient for aqueducts with different height-width ratio is determined by tentative calculation. Modified Housner model inherits the merit and avoids shortcoming of conventional Housner model. Finally the modified model is verified by an example and the accuracy of the model is proved to meet requirement of practical seismic analysis.