The cycle variation characteristics of a port fuel injection hydrogen internal combustion engine (PFI-HICE) have been extensively investigated. The covariance of indicated mean effective pressure (COV imep ) is the best parameter for evaluating the cycle variations in the PFI-HICE. COV imep decreases as fuel–air ratio increases from 1000 to 5500 rpm, and engine speed minimally affects COV imep . The effect of ignition advance angle on COV imep is determined by fuel–air ratio. The ignition advance angles that correspond to the minimum COV imep of the PFI-HICE decrease as fuel–air ratio increases. The effect of ignition advance angle on COV imep diminishes as fuel–air ratio increases. The COV imep of the PFI-HICE rapidly decreases as throttle increases when the throttle is less than 20%. Injection timing only slightly affects COV imep under high-speed conditions, and COV imep increases when hydrogen is injected in intake periods under low-speed conditions. These results indicate that studying COV imep improves the stability of PFI-HICEs.