The work of this paper aimed at investigating the cyclic variations of argon power cycle engine with fuel of hydrogen at lean burn operating conditions. The engine had been modified based on a 0.402 L, single-cylinder diesel engine into spark ignition engine with a port fuel injection system. The influencing factors on the cyclic variations, such as ignition timing, engine speed and compression ratio, were tested in this study. In all tests, the throttle opened at 0%, and the excess oxygen coefficient was maintained at 2.3. The results showed that as the ignition timing retards, CoVPmax and CoV(dp/dφ)max of argon power cycle engine increased, while CoVIMEP decreased firstly and increased afterward. And there is an ignition timing to make the lowest CoVIMEP, which is not consistent with MBT. Under the condition of 900 rpm and MBT, when compression ratio increases from 5.6 to 6.9, both CoVIMEP and CoV(dp/dφ)max of argon power cycle engine were found to decrease, while CoVPmax was found to increase. The engine was also operated with Air-H2 mixtures and a compression ratio of 6.9 for comparison with the condition of argon cycle. For low speed and low load, it was found that Ar-O2-H2 mixtures result in higher IMEP, Pmax and (dp/dφ)max. The significant reduction in CoVIMEP, CoVPmax and CoV(dp/dφ)max indicated that better combustion stability could be achieved when running with Ar-O2-H2 mixtures. Moreover, for operation with Ar-O2-H2 mixtures, there was a very strong correlation between Pmax and its corresponding crank angle; and the absolute value of the correlation coefficient between the two was up to 0.926.