  In the manuscript, we discuss properties of the SDSS J1042-0018 which is a
broad line AGN but mis-classified as a HII galaxy in the BPT diagram (SDSS
J1042-0018 called as a mis-classified broad line AGN). The emission lines
around H$\alpha$ and around H$\beta$ are well described by different model
functions, considering broad Balmer lines to be described by Gaussian or
Lorentz functions. Different model functions lead to different determined
narrow emission line fluxes, but the different narrow emission line flux ratios
lead the SDSS J1042-0018 as a HII galaxy in the BPT diagram. In order to
explain the unique properties of the mis-classified broad line AGN SDSS
J1042-0018, two methods are proposed, the starforming contributions and the
compressed NLRs with high electron densities near to critical densities of
forbidden emission lines. Fortunately, the strong starforming contributions can
be preferred in the SDSS J1042-0018. The mis-classified broad line AGN SDSS
J1042-0018, well explained by starforming contributions, could provide further
clues on the applications of BPT diagrams to the normal broad line AGN.
