This paper investigates the optimal precoding design for uniform linear antenna arrays (ULAs) with the spherical-wave model (SWM). We first model the channel in the MIMO systems with ULAs at both the transmitter (Tx) and receiver (Rx). The-closed-form expressions for the transmit directions and power allocation with the SWM are then derived, respectively. By investigating the inherent properties across the array parameters, including the transceiver distance, the wavelength, array element spacings, Ricean K-factor and the number of Rx antennas,we propose the optimal precoding design. In addition, for the LoS MIMO channels, the entry of correlation matrix can be presented by the sine function. Meanwhile, we derive a maximum capacity criterion by designing the array parameters. Both the analytical and simulation results show that the proposed precoding outperforms the equal power transmission scheme.