A method for determining a sidelink transmission resource, performed by a terminal device (1500, 121, 122), the method comprising: determining a third transmission resource, the third transmission resource comprising a transmission resource for transmitting a physical sidelink shared channel, PSSCH, and the third transmission resource further comprising a first transmission resource for transmitting first sidelink control information, SCI, wherein the third transmission resource is determined according to configuration information received from a network device or is selected by the terminal device (1500, 121, 122) when the terminal device (1500, 121, 122) is a transmitter, or the third transmission resource is determined according to the first SCI when the terminal device (1500, 121, 122) is a receiver; and determining a second transmission resource in the third transmission resource, the second transmission resource comprising a time-domain resource that is the same as and/or adjacent to a time-domain resource for a demodulation reference signal, DMRS, of the PSSCH, the second transmission resource being used for transmitting second SCI, and the second SCI is transmitted in the time-domain resource that is the same as and/or adjacent to the time-domain resource for the DMRS; characterized in that the method further comprises: mapping the second SCI onto the second transmission resource in an order of first frequency domain and then time domain, wherein the time-domain resource for the DMRS is a earliest time-domain resource for the DMRS; and wherein the first SCI comprises a second information field, wherein the second information field is used for determining a size of the second transmission resource. determining a third transmission resource, the third transmission resource comprising a transmission resource for transmitting a physical sidelink shared channel, PSSCH, and the third transmission resource further comprising a first transmission resource for transmitting first sidelink control information, SCI, wherein the third transmission resource is determined according to configuration information received from a network device or is selected by the terminal device (1500, 121, 122) when the terminal device (1500, 121, 122) is a transmitter, or the third transmission resource is determined according to the first SCI when the terminal device (1500, 121, 122) is a receiver; and determining a second transmission resource in the third transmission resource, the second transmission resource comprising a time-domain resource that is the same as and/or adjacent to a time-domain resource for a demodulation reference signal, DMRS, of the PSSCH, the second transmission resource being used for transmitting second SCI, and the second SCI is transmitted in the time-domain resource that is the same as and/or adjacent to the time-domain resource for the DMRS; characterized in that the method further comprises: mapping the second SCI onto the second transmission resource in an order of first frequency domain and then time domain, wherein the time-domain resource for the DMRS is a earliest time-domain resource for the DMRS; and wherein the first SCI comprises a second information field, wherein the second information field is used for determining a size of the second transmission resource. mapping the second SCI onto the second transmission resource in an order of first frequency domain and then time domain, wherein the time-domain resource for the DMRS is a earliest time-domain resource for the DMRS; and wherein the first SCI comprises a second information field, wherein the second information field is used for determining a size of the second transmission resource.