Solidity is a significant design parameter for straight-bladed vertical axis wind turbine (S-VAWT) which has great impacts on aerodynamic performance. Mechanical models at local flow field were built to obtain the relationship between solidity and aerodynamic performance. Numerical investigations were implemented for the dynamic mechanical properties of blade, and efforts were devoted into the influences of radius, chord length and blade number on power coefficient. Experimental investigations were conducted to verify the accuracy and reliability of calculation results. From the results, it was concluded that, self-starting performance at low tip speed ratio was improved by increasing solidity, while the effective region of tip speed ratio to generate high power become smaller. Power coefficient of two and four supporting arms was almost the same when solidity was 0.628, but power output of four was more stable. Parameters of solidity played different role in contribution to power coefficient. Chord length had great effects on increasing the peak of power coefficient, while the blade number will reduce the power coefficient.