The invention relates to an adjustable piston type bidirectional pressure relief valve. The adjustable piston type bidirectional pressure relief valve is characterized by comprising an outer shell, an inner shell, a piston, two springs, two adjustment blocks and two adjusting nuts, wherein the outer shell is transversely arranged; a transversely-through outer shell fluid passage is formed in the outer shell; a fluid passage chamber is disposed in the middle of the outer shell; a separating ring plate is fixedly disposed in the fluid passage chamber; the piston is transversely disposed in the middle of the outer shell fluid passage; the springs, the adjustment blocks and the inner shell are sequentially disposed in the outer shell fluid passage at the left and right sides of the piston from inside to outside; outer ends of the two springs are respectively connected with inner end of the two adjustment blocks; the two adjusting nuts are respectively screwed on outer ends of the two adjustment blocks; and the adjusting nuts are limited in a nut slot. The adjustable piston type bidirectional pressure relief valve has the advantages of simple structure, stable performance, short pressure relief time, rapid speed, high precision and good sealing properties; and bidirectional pressure relief can be carried out.