A needle-switchable type rotary hook sewing machine equipped with a thread routing mechanism, the thread routing mechanism comprising: a thread take-up lever including a sway control end and a thread take-up end; the sway control end bringing the thread take-up end to move upward and downward, and the thread take-up end being provided with a plurality of thread holes, characterized in that the thread routing mechanism also comprising: a cylindrical needle bar case having a rotation axis and a plurality of spaced needle bar holes, and internally defining a hollow space extended from a top to a bottom of the cylindrical needle bar case; the needle bar holes being equally distant from the rotation axis and each having a needle bar received therein; and the needle bars respectively carrying a needle having an eye formed thereon; and a plurality of threads being separately routed through a thread course defined by the thread holes on the thread take-up lever, the hollow space in the cylindrical needle bar case, and the eyes on the needles; a locating disc provided on the bottom of the cylindrical needle bar case, and the locating disc being provided with at least one thread guide hole, through which the threads are extended; a thread pinching unit mounted to an underside of the locating disc; wherein the threads having been routed through the thread course are substantially equally spaced, so that the length of the threads in the thread course would not change due to any needle bar switching operation. a thread take-up lever including a sway control end and a thread take-up end; the sway control end bringing the thread take-up end to move upward and downward, and the thread take-up end being provided with a plurality of thread holes, characterized in that the thread routing mechanism also comprising: a cylindrical needle bar case having a rotation axis and a plurality of spaced needle bar holes, and internally defining a hollow space extended from a top to a bottom of the cylindrical needle bar case; the needle bar holes being equally distant from the rotation axis and each having a needle bar received therein; and the needle bars respectively carrying a needle having an eye formed thereon; and a plurality of threads being separately routed through a thread course defined by the thread holes on the thread take-up lever, the hollow space in the cylindrical needle bar case, and the eyes on the needles; a locating disc provided on the bottom of the cylindrical needle bar case, and the locating disc being provided with at least one thread guide hole, through which the threads are extended; a thread pinching unit mounted to an underside of the locating disc; wherein the threads having been routed through the thread course are substantially equally spaced, so that the length of the threads in the thread course would not change due to any needle bar switching operation. a cylindrical needle bar case having a rotation axis and a plurality of spaced needle bar holes, and internally defining a hollow space extended from a top to a bottom of the cylindrical needle bar case; the needle bar holes being equally distant from the rotation axis and each having a needle bar received therein; and the needle bars respectively carrying a needle having an eye formed thereon; and a plurality of threads being separately routed through a thread course defined by the thread holes on the thread take-up lever, the hollow space in the cylindrical needle bar case, and the eyes on the needles; a locating disc provided on the bottom of the cylindrical needle bar case, and the locating disc being provided with at least one thread guide hole, through which the threads are extended; a thread pinching unit mounted to an underside of the locating disc; wherein the threads having been routed through the thread course are substantially equally spaced, so that the length of the threads in the thread course would not change due to any needle bar switching operation.