In consideration of low nonlinearity and maintaining of loss and dispersion when few-mode fiber is operated in single mode, the coexistence scheme of quantum-classical signals based on few-mode fiber operated in single mode was put forward. The coexistence model of quantum-classical signals based on few-mode fiber operated in single mode was built by Optisystem. The transmission performance of the model was analysed and compared with the existing model based on single-mode fiber. The result shows that the nonlinearity and signal crosstalk in existing model have been reduced efficiently in the proposed model. The bit error rate is two orders of magnitude lower than existing model and the transmission quality is improved obviously. It is suitable to apply the proposed model to massive network realization of quantum private communication.