The purpose of this study is to investigate the effects of electro-acoustic hearing in cochlear implant (CI) simulation on Mandarin speech recognition under background noise. This study modeled the ACE strategy with 900 Hz stimulation rate and 8 stimulation channels, used the white noise vocoder for CI processing, and simulated HA signals with a low-pass filter (cut off frequency 500 Hz). Disyllabic Chinese words and sentences were processed with the ACE with the speech-shaped-noise (SSN) as the background noise to test on four signal-to-noise ratios (SNR, 10 dB, 5 dB, 0 dB, and -5 dB) for both the CI only and CI+HA conditions. There were eight normal hearing (NH) adults participating in this simulation experiment. For comparison purpose, ten prelingually deafened CI subjects were tested on four different SNR conditions (Quiet, 10 dB, 5 dB, 0 dB) with disyllabic words and sentences for the same test conditions. Our simulation study showed that the word recognition rates of the NH subjects on the CI only condition decreased with the descending SNR (86%, 76%, 50%, 19%). However, the word recognition rates of the CI+HA stimulation on NH subjects were 99%, 97% 91%, and 44% for the descending SNR, respectively. In addition, the sentence recognition results of the NH subjects indicated that the speech recognition rate decreased (88%, 68%, 32%, 4%) with the descending SNR for the CI only condition. The test scores all rose up and were statistically significant (100%, 99%, 96%, 67%, p<0.001) for the CI+HA condition. Our clinical results show that the speech (words and sentence) recognition rate increases with the electro-acoustic hearing (CI+HA) and increasing SNR, but not statistically significant. However, both our simulation and clinical results suggest that Mandarin speech recognition could be enhanced if more speech information are provided from the HA to the CI users.