MnSi1.70+x(x=0, 0.05, 0.1, 0.15) compounds have been prepared by induction melting-annealing procedure combined with spark plasma sintering method. The phase composition and the thermoelectric properties of higher manganese silicide (HMS) with different Si contents are investigated. The results indicate that the samples with x＜0.1 include HMS phase and MnSi phase, and the relative content of MnSi phase decreases with x value increasing. The sample with x=0.1 is single phase HMS. The phase compositions of the sample with x＞0.1 are HMS and Si. As x value inereases the electrical conductivity of the sample gradually decreases, while the Seebeck coefficient increases because metallic MnSi phase decreases. The carrier concentration and the effective mass of the sample at room temperature decrease and the carrier mobility increases with x value increasing. In the sample with x=0.1, the impurity phase content is the least, which results in the lowest thermal conductivity and a minimum value of 2.25 W ·m-1K-1 at 800 K. The maximum ZT value of 0.45 is obtained at 850 K for MnSi1.80.