Abstract: The present invention provides an acryloylmorpholine polymer and the use thereof and a filtrate reducer for drilling fluid. The acryloylmorpholine polymer comprises structural units expressed by formula (1), structural units expressed by formula (2), and structural units expressed by formula (3), wherein, at least a part of the structural units expressed by formula (2) can be bonded with at least a part of the structural units expressed by formula (3) into cross-linked structural unit expressed by formula (4); wherein, R1-R9 are H or C1-C3 linear or branched alkyl respectively, y is an integer within 1-5 range, M is H or an alkali metal element, X is O or NH, and R10 is C1-C5 linear or branched alkylidene. The acryloylmorpholine polymer and filtrate reducer for drilling fluid have outstanding filtrate reduction and viscosity increasing effects.