Subsynchronous oscillations (SSOs) induced by the integration of high renewable energy penetration have significantly impacted the operation of power systems. This article proposed an enhanced matrix pencil method (MPM) for online monitoring of SSO using synchrophasors. To address the issue of eigenvalues of complex-domain matrix pencil not satisfying the conjugate frequency constraints of the synchrophasors, the complex Hankel matrix of synchrophasors is transferred to the field of real numbers. This improvement can shorten the data window of parameter identification to 200 ms while maintaining the computational efficiency of MPM. In addition, to ensure the identification accuracy by fully utilizing the information of complex-domain synchrophasors, the feasibility of constructing a new real-domain Hankel matrix with the combination of the separate real and imaginary parts of the complex Hankel matrix is proved. Compared with the existing MPM-based methods, the proposed enhanced MPM achieves better accuracy for parameter identification of SSOs while significantly reducing the computational burden in practical applications.