Objective To compare the application value of multi-slice spiral CT and ultrasonography in patients with acute appendicitis before operation. Methods 72 inpatient with acute appendicitis who were admitted into the hospital during April 2013 to April 2015 were treated as the research objects. All of the patients underwent ultrasonography and multi-slice spiral CT examination. The accurate rates and the results of the diagnosis of different types of appendicitis were compared between the two groups. Results Among the 72 patient with acute appendicitis, there were 48 cases correctly diagnosed by ultrasonography and 24 cases missed diagnosed. The accuracy was 66.7% (48/72). There were 66 cases correctly diagnosed by multi-slice spiral CT and 6 cases missed diagnosed. The accuracy was 91.7% (66/72). The comparisons were statistically significant (χ2=13.642, P=0.000＜0.05). In different types of appendicitis, the accurate diagnosis rate of both the two examination methods for gangrenous appendicitis was 100%. The comparison was not statistically significant (P>0.05). The accurate diagnosis rates of CT for edema and suppurative appendicitis were higher than those of ultrasonography. The comparison was statistically significant (P<0.05). Conclusion Compared with ultrasonography, multi slice spiral CT is of greater application value in acute appendicitis before operation. The diagnostic accuracy of multi slice spiral CT is higher and it can effectively reflect the position, length, thickness, direction, adhesion and peripheral exudation of the appendix, which is good for the implementation of operation. The clinical application value is high.