A method for triggering a Buffer Status Reporting, BSR, the method comprising: determining, by a user equipment, the size of padding resources when the user equipment composes a D2N MAC PDU, wherein the D2N MAC PDU is a device to network media access control protocol data unit; and deciding, by the user equipment, whether to trigger a D2D padding BSR, according to the size of the padding resources, and the priority of D2D padding BSR MAC CE being higher or lower than the priority of D2N padding BSR MAC CE, wherein the D2D padding BSR MAC CE is a media access control layer control element for carrying a device to device communication padding buffer status reporting, and the D2D padding BSR is a device to device communication padding buffer status reporting; wherein determining the size of the padding resources comprises: subtracting the following resources from uplink resources of the user equipment in a sub-frame where the D2N MAC PDU is located; resources occupied by other D2N MAC CE than D2N MAC CE for carrying a D2N padding BSR, wherein the occupied resources comprise resources occupied by a MAC sub-header and a payload; resources occupied by logical channel data over a D2N link other than an Uplink Common Control Channel, UL-CCCH, wherein the occupied resources comprise resources occupied by a MAC sub-header and a payload; and resources occupied by other D2D MAC CE than D2D MAC CE for carrying a D2D padding BSR, wherein the occupied resources comprise resources occupied by a MAC sub-header and a payload; wherein the resources are subtracted from the uplink resources of the user equipment in the sub-frame where the D2N MAC PDU is located, in a first priority order from high priority to low priority as follows: the resources occupied by other D2N MAC CE than D2N MAC CE for carrying the D2N padding BSR, the resources occupied by logical channel data over the D2N link other than the UL-CCCH, and the resources occupied by other D2D MAC CE than D2D MAC CE for carrying the D2D padding BSR. determining, by a user equipment, the size of padding resources when the user equipment composes a D2N MAC PDU, wherein the D2N MAC PDU is a device to network media access control protocol data unit; and deciding, by the user equipment, whether to trigger a D2D padding BSR, according to the size of the padding resources, and the priority of D2D padding BSR MAC CE being higher or lower than the priority of D2N padding BSR MAC CE, wherein the D2D padding BSR MAC CE is a media access control layer control element for carrying a device to device communication padding buffer status reporting, and the D2D padding BSR is a device to device communication padding buffer status reporting; wherein determining the size of the padding resources comprises: subtracting the following resources from uplink resources of the user equipment in a sub-frame where the D2N MAC PDU is located; resources occupied by other D2N MAC CE than D2N MAC CE for carrying a D2N padding BSR, wherein the occupied resources comprise resources occupied by a MAC sub-header and a payload; resources occupied by logical channel data over a D2N link other than an Uplink Common Control Channel, UL-CCCH, wherein the occupied resources comprise resources occupied by a MAC sub-header and a payload; and resources occupied by other D2D MAC CE than D2D MAC CE for carrying a D2D padding BSR, wherein the occupied resources comprise resources occupied by a MAC sub-header and a payload; wherein the resources are subtracted from the uplink resources of the user equipment in the sub-frame where the D2N MAC PDU is located, in a first priority order from high priority to low priority as follows: the resources occupied by other D2N MAC CE than D2N MAC CE for carrying the D2N padding BSR, the resources occupied by logical channel data over the D2N link other than the UL-CCCH, and the resources occupied by other D2D MAC CE than D2D MAC CE for carrying the D2D padding BSR. subtracting the following resources from uplink resources of the user equipment in a sub-frame where the D2N MAC PDU is located; resources occupied by other D2N MAC CE than D2N MAC CE for carrying a D2N padding BSR, wherein the occupied resources comprise resources occupied by a MAC sub-header and a payload; resources occupied by logical channel data over a D2N link other than an Uplink Common Control Channel, UL-CCCH, wherein the occupied resources comprise resources occupied by a MAC sub-header and a payload; and resources occupied by other D2D MAC CE than D2D MAC CE for carrying a D2D padding BSR, wherein the occupied resources comprise resources occupied by a MAC sub-header and a payload; wherein the resources are subtracted from the uplink resources of the user equipment in the sub-frame where the D2N MAC PDU is located, in a first priority order from high priority to low priority as follows: the resources occupied by other D2N MAC CE than D2N MAC CE for carrying the D2N padding BSR, the resources occupied by logical channel data over the D2N link other than the UL-CCCH, and the resources occupied by other D2D MAC CE than D2D MAC CE for carrying the D2D padding BSR. the resources occupied by other D2N MAC CE than D2N MAC CE for carrying the D2N padding BSR, the resources occupied by logical channel data over the D2N link other than the UL-CCCH, and the resources occupied by other D2D MAC CE than D2D MAC CE for carrying the D2D padding BSR.