A power transmission apparatus with over-loading protection and power-saving mechanism, comprising: a switch module, comprising: a first switch circuit, coupled between a power input module and a power supply port to receive an AC power provided by a city power system from the power input module, and controlled by a first control signal (SW_EMR) to transmit the AC power to the power supply port; a second switch circuit, coupled to the power input module to receive the AC power; and a protection circuit, coupled between the second switch circuit and the power supply port, wherein the second switch circuit is controlled by a second control signal (SW_SSR) to transmit the AC power to the power supply port through the protection circuit, wherein the protection circuit is controlled by the second control signal (SW_SSR) to detect a load power of the power supply port when the second switch circuit is turned on, and the protection circuit generates the first control signal (SW_EMR) to enable the first switch circuit when an instantaneous variation of the load power is greater than a predetermined over-loading threshold so as to protect the second switch circuit at an on-state. a switch module, comprising: a first switch circuit, coupled between a power input module and a power supply port to receive an AC power provided by a city power system from the power input module, and controlled by a first control signal (SW_EMR) to transmit the AC power to the power supply port; a second switch circuit, coupled to the power input module to receive the AC power; and a protection circuit, coupled between the second switch circuit and the power supply port, wherein the second switch circuit is controlled by a second control signal (SW_SSR) to transmit the AC power to the power supply port through the protection circuit, wherein the protection circuit is controlled by the second control signal (SW_SSR) to detect a load power of the power supply port when the second switch circuit is turned on, and the protection circuit generates the first control signal (SW_EMR) to enable the first switch circuit when an instantaneous variation of the load power is greater than a predetermined over-loading threshold so as to protect the second switch circuit at an on-state. a first switch circuit, coupled between a power input module and a power supply port to receive an AC power provided by a city power system from the power input module, and controlled by a first control signal (SW_EMR) to transmit the AC power to the power supply port; a second switch circuit, coupled to the power input module to receive the AC power; and a protection circuit, coupled between the second switch circuit and the power supply port, wherein the second switch circuit is controlled by a second control signal (SW_SSR) to transmit the AC power to the power supply port through the protection circuit, wherein the protection circuit is controlled by the second control signal (SW_SSR) to detect a load power of the power supply port when the second switch circuit is turned on, and the protection circuit generates the first control signal (SW_EMR) to enable the first switch circuit when an instantaneous variation of the load power is greater than a predetermined over-loading threshold so as to protect the second switch circuit at an on-state.