The invention relates to a reciprocating shaft magnetic liquid sealing structure, which comprises a first bearing, a first magnetic-isolated ring, a first pole piece, a first O-shaped rubber gasket ring, a permanent magnet, a second O-shaped rubber gasket ring, a second pole piece, a second magnetic-isolated ring and a second bearing, which are sequentially and closely propped against an external nested inner lug boss, wherein an end cover is fixed on an outer jacket through a bolt, and the second bearing is compressed. The inner annular surface of the second pole piece (13) is provided with a left, a middle and a right counter bores, elastic rings (T) with the quantity of N+1 and trapezoid sealing gears (C) are arranged at intervals from each other to be closely arranged inside the middle counter bore, N is a positive integer of 1 to 8, the trapezoid sealing gears and the elastic rings, which are closely lined at intervals, are fixedly connected with the second pole piece in a threading way through bolts and retainer rings (15), and the trapezoid sealing gears with the quantity of N are lined up in the expansion direction of the identical inner holes; and the structure of the first pole piece (7) is completely identical to that of the second pole piece. The problems of the conventional reciprocating shaft magnetic liquid sealing structure that the magnetic liquid runs off, the sealing service life is shortened, and the leakage rate is increased can be solved.