The Shaymen, who were playing their fifth game in 12 days, were caught cold as Tahvon Campbell, Jack Stevens and a Tylor Golden own goal had them three down inside 38 minutes.
Jack Evans and substitute Florent Hoti scored to give the Yorkshire side real hope, but they then saw a Rob Harker header hit the bar, and Jamey Osborne settled it with a fourth goal for Moors in the 86th minute.
Solihull have already booked their first-ever Wembley visit, as they face Gateshead in the FA Trophy final on 11 May, but victory at The Hive on Saturday would also see them play there on 5 May with a league place at stake.
The Shaymen went into the game with 48 hours’ notice after the National League’s decision to exclude Gateshead from the play-offs after their ground failed to meet Football League criteria.
They also had to play four games last week after postponements due to the toll heavy rain and the Halifax Panthers rugby league team had taken on their Shay pitch.
They only secured seventh place with a win at Eastleigh on Saturday and that hectic schedule seemed to have an effect as Solihull dominated the early stages.
Campbell saw his shot deflect past keeper Sam Johnson and Stevens, after missing a great chance, got the final touch to another Campbell shot to double the lead.
It all seemed to be over as Campbell again let fly, and his deflected shot was turned past his own goalkeeper by Golden.
Evans headed home from a corner in first half added time, and sub Hoti, a Kosovo under-21 international, crashed a 25-yard effort in off the underside of the bar as Halifax found reserves of strength to fight back strongly.
Harker then headed another big opportunity against the underside of the bar and the outstanding Osborne made sure for the home side as he squeezed through two challengers and forced his shot between Johnson and his near post with four minutes of normal time to go.
