A mapping study of IRAS 05553+1631 was performed with 12CO J= 3 –2 and 13CO J= 2 –1 lines observed by the KOSMA 3-m telescope. A core with a size of 0.65 pc and with a local thermodynamic equilibrium mass of 120 M⊙ was defined by mapping with the 13CO J= 2 –1 line. We have identified a bipolar outflow with 12CO J= 3 –2. For accuracy in the calculation of outflow parameters, overcoming the projection effect is important. We propose a new method to directly calculate the inclination angle θ. We establish two basic equations with the help of an outflow contour diagram and finally obtain the ‘angle function’ and the ‘angle equation’ to derive θ. We apply our method to the outflow of IRAS 05553+1631, finding that θblue is 73° and θred is 78°. Compared to the parameters initially estimated under the assumption of a 45° inclination angle, the newly derived parameters are changed by different factors. For instance, the time-scales for the blue and the red lobes became smaller by 0.31 and 0.21, respectively. Larger influences apply to the mechanical luminosity, driving force and mass-loss rate. Comparisons between parameters before and after the correction show that the effect of the inclination angle cannot be neglected.