The invention relates to a method for acquiring neutron angular flux density in a nuclear fuel assembly. The method comprises the following steps: 1, calculating value of a primary function; 2, calculating integral of the primary function and angle variable; 3, establishing a wavelet unwrapping equation in the assembly; 4, processing assembly boundary conditions; 5, calculating the neutron angular flux density; 6, establishing the wavelet unwrapping equation with allowance; 7, correcting the neutron angular flux density; and 8, judging whether the neutron angular flux density meets the precision demand or not. According to the invention, argument variable of neutron angular flux density is unwrapped by using a one-dimensional primary function to reduce the calculation scale. By means of adopting the assembly boundary unwrapping and the unwrapping within the assembly respectively, the fuel assembly boundary is unwrapped in areas to avoid calculation of redundancy unwrapping coefficient. As the neutron angular flux density and the allowance are respectively processed, two-time equal coupling scales are just calculated, so that the unwrapping order is relatively and simply improved. Under the premise that approximate computational accuracy is realized, the coupling coefficient is prevented from square increase along with precision improvement, and the calculating efficiency is improved.