The eigenvalues of a time-delay system are infinite, and exhibit complex distributions. The classical definite integral method is an effective approach for analyzing the stability of multi-time-delay systems. However, it cannot directly solve the modal frequencies, i.e., the imaginary parts of the eigenvalues of the system, and instead requires first determining the real parts and then applying additional techniques, such as two-dimensional Newton iteration to solve the modal frequencies. For most stable systems, modal frequency is often of greater concern, and indirect determination introduces unnecessary steps and increases computational complexity. Therefore, this article extends the definite integral method by using a new integration path and a new characteristic root translation direction, which can directly solve the modal frequency of time-delay systems, while retaining the advantages of the classical definite integral method, such as being suitable for multi time-delay systems, simple programming, and high efficiency. The paper verifies the wide applicability and the effectiveness of the proposed method for calculating the modal frequencies of time-delay systems through two engineering examples.