The commuting sequence of ordinary STATCOM is analyzed in this paper， which shows that when a STATCOM inputs reactive power， its turn-off devices can be replaced by thyristors. A prototype of such thyristor based STATCOM is built， including a digital controller based on FPGA and DSP which can provide high-precision firing pulses for thyristors. Experimental results show that the thyristor based STATCOM can input reactive power by adjusting its fire angle and has same characteristics as ordinary STATCOM within its operating range. Hence it can be used for static var compensation in power systems.