The phrase "Kingdom of Heaven" occurs only in Matthew's Gospel and is equivalent to the "Kingdom of God" as the following comparisons show.
Matthew 4 v 17 and Mark 1 v 14 and 15:
17 From that time, Jesus began to preach, and to say, “Repent! For the Kingdom of Heaven is at hand.”
14 Now after John was taken into custody, Jesus came into Galilee, preaching the Good News of God’s Kingdom, 15 and saying, “The time is fulfilled, and God’s Kingdom is at hand! Repent, and believe in the Good News.”
Matthew 19 v 13 and 14 and Mark 10 v 13 and 14:
13 Then little children were brought to him, that he should lay his hands on them and pray; and the disciples rebuked them. 14 But Jesus said, “Allow the little children, and don’t forbid them to come to me; for the Kingdom of Heaven belongs to ones like these.”
13 They were bringing to him little children, that he should touch them, but the disciples rebuked those who were bringing them. 14 But when Jesus saw it, he was moved with indignation, and said to them, “Allow the little children to come to me! Don’t forbid them, for God’s Kingdom belongs to such as these.
Matthew 5 v 3 and Luke 6 v 20:
3 “Blessed are the poor in spirit,
for theirs is the Kingdom of Heaven.
20 He lifted up his eyes to his disciples, and said,
“Blessed are you who are poor,
God’s Kingdom is yours.
Matthew 11 v 11 and Luke 7 v 28:
11 Most certainly I tell you, amongst those who are born of women there has not arisen anyone greater than John the Baptiser; yet he who is least in the Kingdom of Heaven is greater than he.
28 “For I tell you, amongst those who are born of women there is not a greater prophet than John the Baptiser, yet he who is least in God’s Kingdom is greater than he.”
Matthew 13 v 10 and 11 and Luke 8 v 9 and 10:
10 The disciples came, and said to him, “Why do you speak to them in parables?”
11 He answered them, “To you it is given to know the mysteries of the Kingdom of Heaven, but it is not given to them.
9 Then his disciples asked him, “What does this parable mean?”
10 He said, “To you it is given to know the mysteries of God’s Kingdom, but to the rest in parables; that ‘seeing they may not see, and hearing they may not understand.’
We look at the Kingdom of God in another theme.