In this paper, we propose an iterative detecting and decoding method in LTE Downlink OFDM system based on reference aided channel estimation. Estimates of the complex channel gain and variance of the additive noise are derived first from known reference symbols and channel estimate filter. After turbo decoding, the decoded bits have been obtained. In order to obtain estimates of channel gain more accuracy, we adopted more reference symbols which modulate the decoded bits at the receiver again to estimate the channel frequency response. Also the mapping position of the OFDM symbols is consistent with first transmission. Through estimation of the channel iteratively, we can use more systems bits as iterative reference symbols. Simulation results shows that through the iterative channel estimation, the initial insert reference symbols have been reduced, the accuracy of channel estimation improved effectively and the bits error rate of the OFDM system can approach the perfect channel estimates.