The invention provides a zero alignment type impact side dilatometer, wherein a zero calibration block and a benchmark support are arranged on a base, a digital display dial indicator is arranged on the benchmark support and provided with a circular plane measuring head; the base and the benchmark support are fixed through a first clamp nut, and the digital display dial indicator and the benchmarksupport are fixed through a second clamp nut; a use method comprises the following steps: 1, aligning zero; 2, enabling one side of an impact testing piece to cling to the circular plane measuring head of the digital display dial indicator, recording the reading LP1 of the digital display dial indicator; 3, enabling the other side of the impact testing piece to cling to the circular plane measuring head of the digital display dial indicator, recording the reading LP2 of the digital display dial indicator; and 4, adding the reading in the step 2 and the reading in the step 3 to obtain the impact test side swell capacity. The defect of low measurement accuracy of a vernier caliper is overcome, and the zero alignment is added to avoid the problem of zero misalignment caused by abrasion of adetection surface of the benchmark support after long-term use.