In order to fit the sin wave of Strap-down north seeking system and calculate the angle between the start position and the real north accurately

the principle of the system are introduced

and the factors that influence the precision are analyzed. Least square method and back-propagation neural network are adopted separately. Experimental results indicate that the back-propagation neural network is more precision than the least square method

the sum of errors is 0.06

the squared error of errors is 34.45

both of the method get the same average of phases in six measurements

the squared error of BP neural network is 8″

it’s more accurate than the result of the least square method. The back-propagation neural network can satisfy the system precision requirements of curve-fit.