According to the present invention, there is proposed a method for HARQ process allocation for DL SPS transmission between a base station and an UE, and a system thereof. The method comprises steps of: at the base station side, configuring a HARQ process preserved for the SPS transmission and its related control information based on RRC or other control instructions from the upper layer, and transmitting the configured HARQ process and its related control information to the UE; sending down an SPS-CRNTI-based PDCCH to activate SPS configuration and indicating a HARQ process for a first SPS transmission before the first SPS transmission; determining a HARQ process allocated to the current transmission, and allocating the HARQ process preserved for the SPS transmission to possible DS transmissions when the SPS transmission is in idle; and determining a type for transmission or retransmission to be carried in the current HARQ process based on a preset criteria, then performing the determined type of transmission or retransmission, and correspondingly sending a PDCCH down; at the UE side, receiving the RRC or other control instructions from the base station; receiving PDCCH from the base station to activate SPS configuration and obtaining the time for the first SPS transmission and used HARQ process; receiving respective data transmission or retransmission and possible PDCCH from the base station; and determining a type for the received data transmission or retransmission based on a preset criteria, so as to perform respective data combination. The method and system according to the present application achieve HARQ process allocation for DL SPS transmission, while improving the DS transmission chance and reducing the ambiguity between different SPS transmissions and between SPS transmission and DS transmission.