It has become popular to think of the judgment as a judgment of God—one in which God is on trial. That view has often been read into the expression "his judgment" in Revelation 14:7.
The Greek word used for “judgment” in Revelation 14:7 is krísis, the primary definition of which is:
1. judging, judgment—a. of the activity of God or the Messiah as judge, esp. on the Last Day” (A Greek-English Lexicon of the New Testament by Arndt and Gingrich, p. 453).
The SDA Bible Commentary on Revelation 14:7 has this to say about the word “judgment” as used in that verse: “Gr. krisis, 'the act of judging,’ contrasted with krima, ‘the sentence of judgment’.”
We find the same word in John 5:27 where Jesus claims "authority to execute judgment.” It means to “act as judge” (Arndt and Gingrich, p. 453).
The lexicon actually cites Revelation 14:7 as a typical example of this word, and translates the phrase in question as: “the hour when he is to judge Rv 14:7” (Ibid.).
So it is clear that God is the one doing the judging in this verse.
“Krisis may indicate either the act of investigating a case or the act of carrying out the sentence” (SDA Bible Commentary, Vol. 7, p. 849).
Revelation 14:7 is clearly talking about the investigative judgment (as opposed to the later judgment of the wicked) because it says that it “is come” (present tense in the context of the proclamation of the first angel’s message).
To find out what the investigative judgment is all about, we can read the chapter “Facing Life’s Record” in The Great Controversy. The whole chapter describes this judgment. It can be summarized in the second paragraph of the chapter:
"Thus was presented to the prophet's vision the great and solemn day when the characters and the lives of men should pass in review before the Judge of all the earth, and to every man should be rendered 'according to his works.' The Ancient of Days is God the Father. Says the psalmist: 'Before the mountains were brought forth, or ever Thou hadst formed the earth and the world, even from everlasting to everlasting, Thou art God.' . It is He, the source of all being, and the fountain of all law, that is to preside in the judgment. And holy angels as ministers and witnesses, in number 'ten thousand times ten thousand, and thousands of thousands,' attend this great tribunal” (GC 479).
It is very clear—from the language used in the text, and also from The Great Controversy—that Revelation 14:7 is not about God being judged, but rather that mankind is being judged by God.