A method of clock transmission between networks, comprising: acquiring a second information corresponding to a clock transferred by a first network equipment based on a first protocol, and the second information corresponding to a clock transferred by a second network equipment based on a second protocol; performing a source selection in a united way on the clock transferred by the first network equipment based on the first protocol and the clock transferred by the second network equipment based on the second protocol according to the obtained second information; and transmitting the second information corresponding to a selected clock source based on the second protocol according to the clock of the selected clock source; wherein the acquiring the second information corresponding to the clock transferred by the first network equipment based on the first protocol comprises: parsing a protocol frame transferred by the first network equipment based on the first protocol to acquire a first information corresponding to the clock transferred by the first network equipment; and converting the first information corresponding to all clocks transferred by the first network equipment to the second information according to a corresponding relation between the first information and the second information; and wherein the first protocol comprises a Precision Time Protocol, PTP, the second protocol comprises a synchronous digital hierarchy, SDH, protocol or a synchronous optical network, SONET, protocol, the first information is a PTP clock class information, and the second information is a synchronization status message, SSM; or the first protocol comprises an SDH protocol or a SONET protocol, the second protocol comprises a PTP, the first information is an SSM, and the second information is a PTP clock class information. acquiring a second information corresponding to a clock transferred by a first network equipment based on a first protocol, and the second information corresponding to a clock transferred by a second network equipment based on a second protocol; performing a source selection in a united way on the clock transferred by the first network equipment based on the first protocol and the clock transferred by the second network equipment based on the second protocol according to the obtained second information; and transmitting the second information corresponding to a selected clock source based on the second protocol according to the clock of the selected clock source; wherein the acquiring the second information corresponding to the clock transferred by the first network equipment based on the first protocol comprises: parsing a protocol frame transferred by the first network equipment based on the first protocol to acquire a first information corresponding to the clock transferred by the first network equipment; and converting the first information corresponding to all clocks transferred by the first network equipment to the second information according to a corresponding relation between the first information and the second information; and wherein the first protocol comprises a Precision Time Protocol, PTP, the second protocol comprises a synchronous digital hierarchy, SDH, protocol or a synchronous optical network, SONET, protocol, the first information is a PTP clock class information, and the second information is a synchronization status message, SSM; or the first protocol comprises an SDH protocol or a SONET protocol, the second protocol comprises a PTP, the first information is an SSM, and the second information is a PTP clock class information. parsing a protocol frame transferred by the first network equipment based on the first protocol to acquire a first information corresponding to the clock transferred by the first network equipment; and converting the first information corresponding to all clocks transferred by the first network equipment to the second information according to a corresponding relation between the first information and the second information; and wherein the first protocol comprises a Precision Time Protocol, PTP, the second protocol comprises a synchronous digital hierarchy, SDH, protocol or a synchronous optical network, SONET, protocol, the first information is a PTP clock class information, and the second information is a synchronization status message, SSM; or the first protocol comprises an SDH protocol or a SONET protocol, the second protocol comprises a PTP, the first information is an SSM, and the second information is a PTP clock class information.