A modular support assembly for a solar power system includes a plurality of base units each of which includes a base frame having first and second tube members, and a plurality of connection units each of which interconnects two adjacent ones of the base units. Each connection unit includes two sleeve members and a plurality of fasteners. Each sleeve member has a tubular portion sleeved on one end of the second tube member of one of the two adjacent ones of the base units, and a blind flange connected to the tubular portion and closing the one end of the second tube member. The blind flanges abut against each other and are fastened by the fasteners.