The invention relates to a semi-bridge type MMC sub module and a short-circuit protection method of an upper switch tube. The semi-bridge type MMC sub module comprises the upper switch tube, a lower switch tube, a bypass switch and a direct current supporting capacitor and also comprises at least one energy-saving branch connected at two ends of the direct current supporting capacitor in parallel;at least one energy-consuming resistor and at least one controllable switch which is conducted when the upper switch tube is in short circuit are serially arranged on the energy-consuming branch. Themodule prevents the condition that components and connecting bus bars in the sub module are damaged by a short-circuiting large electrodynamic force formed by capacitive discharge after the sub module is bypassed by the bypass switch when the upper switch tube is in short circuit, the apparatuses and connecting bus bars in the loop are protected, the normal operation of the system is not affected, and the self protection of the sub module is achieved. The semi-bridge type MMC sub module provided by the invention is simple and reliable and has a relatively high engineering practical value.