The finite impulse response (FIR) filters in the space radiation environment probably face the single event upset (SEU), making unexpected results. To avoid that situation, the traditional triple module redundancy (TMR) technology is usually applied. At the same time, however, it brings high cost of area and power. For this reason, an improved TMR (ITMR) structure for FIR filters is proposed in this paper. Simulation shows that the design can achieve the same performance with much less resources. Based on traditional technique TMR, the design reports an improved TMR (ITMR) structure by simplify the two redundancy modules, the advantage that it has the same performance but costs less resources can be reflect by the simulation and synthesis clearly.