A demand response resource aggregation optimization model and method under invitation mode is proposed from the perspective of load integrators. Firstly, based on the actual situation of demand response transactions in some provinces and regions in China, the mode of day-ahead invitation response and the aggregation agent mechanism of load integrators for users are analyzed. Then, based on the mechanism conditions for organizing, assessing, and compensating for the demand response of the day-ahead invitation, and taking into account the characteristics of user resource response, effective response capacity authentication, and the impact of the revenue and assessment cost allocation ratio between load integrators and users, an aggregation optimization model is constructed to better adapt to the needs of load integrators for making day-ahead invitation response decisions. Aiming at the nonlinear coupling relationship of decision variables in the model, intermediate variables and logical constraints are introduced for linearization processing, which is then transformed into a mixed integer programming problem to reduce the difficulty of solving. The analysis of numerical examples shows that the aggregation optimization of different types of response resources can help to improve the expected returns of load integrators in the day-ahead invitation response, and can provide more detailed information for the analysis of the limit capacity of load integrators to compatible with different quality resources, which verifies the effectiveness of the model and method.