In order to improve the temperature and salt resistance of polymer fluid loss additive and the compatibility with high density and high solid phase deep well drilling fluid system，the self-made hexene monomer TDED was used as a crosslinking agent， and acrylamide （AM）， 2-acrylamide-2-methylpropanesulfonic acid （AMPS） and N-vinylpyrrolidone （NVP） were subjected to free radical copolymerization to prepare a micro-crosslinking copolymer fluid loss additive PTAPN. The structure of the product was characterized by infrared spectrometer. The temperature and salt tolerance of PTAPN and the compatibility with different density drilling fluids were studied. The results showed that the molecular structure of the product was consistent with the design. PTAPN had good fluid loss performance in high temperature and high salinity environments. After adding 2% PTAPN，the viscosity of fresh water and composite brine base slurry increased before and after aging at 240℃ ，and the fluid loss greatly reduced. PTAPN had good compatibility with different density water-based drilling fluids，which could effectively control the rheology and fluid loss of heavy drilling fluid with a density of 2.30 g/cm3 in high temperature environment. When the aging temperature was 240℃，the API fluid loss and high temperature and high pressure fluid loss of weighting drilling fluid was 2.6 and 12.6 mL，respectively，which was much smaller than that of drilling fluid containing conventional linear polymer fluid loss additive. PTAPN was suitable as a fluid loss additive for high temperature and high density drilling fluid systems.