In order to study evolution of real-time working resistance of hydraulic support with roof breaking in fully-mechanized working face of medium-thickness coal seam, a mechanical model of main roof was established based on elastic foundation beam, and law of main roof movement was analyzed. It was pointed out that breaking position of overlying strata was in front of working face, and analytical solution of pre-breaking distance was given. The roof breaking form of the initial weighting and period weighting of working face were analyzed combined with engineering practice, and calculation formulas of real-time working resistance of support during period weighting were obtained. The research results are as following. Main roof fractures twice in a single weighting cycle. Working resistance of support is a nonlinear function of suspension length of main roof before the first breaking. When the suspension length is equal to limit breaking distance, working resistance of support reaches the maximum value with main roof breaking. Before the second breaking of main roof, working resistance of support increases with working face advance distance as a quadratic function, and reaches the maximum value with main roof breaking.