The invention relates to the technical field of assembling, in particular to a tightening and lengthening transition mechanism. The tightening and lengthening transition mechanism comprises a tightening device and a tightening shaft on the tightening device. The tightening and lengthening transition mechanism further comprises a sleeve, a transition sleeve and a counter force transition sleeve, wherein the sleeve is used for assembling a fastener, one end of the transition sleeve is fixedly connected with the sleeve, the other end of the transition sleeve is fixedly connected with the tightening shaft, the counter force transition sleeve is arranged outside the sleeve and the transition sleeve, one end of the counter force transition sleeve is connected with the tightening device, and a counter force block is arranged above the other end of the counter force transition sleeve. The tightening and lengthening transition mechanism is small in size, low in weight, simple in structure, convenient to maintain, safe and reliable, the fastener is conveniently and accurately assembled, and use by an operator is protected and is convenient.