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Synthesis of multi-mode electric-mechanical variable transmission (EVT) mainly involves two contents: the topology of planetary gear mechanism (PGM) and the determination of their characteristic parameters. This article deals with the computationally intensive problems caused by numerous potential schemes and proposes an automatic and systematic design process for multi-mode EVTs based on 3-row PGM. First, all the non-isomorphic 4-degree-of-freedom (4-DOF) topologies are enumerated by combining the modified digraph model with the determinants of their adjacency matrices. Second, the rules with guiding significance for configuring shift elements and motor/generators (M/Gs) are summarized to eliminate all infeasible configurations. And all the mechanical points (MPs) that come from the kinematic equations play an important role in the selection of new schemes. Third, the method of Monte Carlo simulation handles the problem of solving many different forms of multivariate nonlinear functions to sort the rational mode sequences. Finally, the characteristic parameters of each planetary gear set are optimized by NSGA-II. The feasibility of the method is verified by synthesizing six novelty 3-mode EVTs and it is also applicable to similar problems.