Context : The spiral structure of our Milky Way Galaxy is not yet known .
HII regions and giant molecular clouds are the most prominent spiral tracers .
Models with 2 , 3 or 4 arms have been proposed to outline the structure of our Galaxy .

Aims : Recently , new data of spiral tracers covering a larger region of the Galactic disk have been published .
We wish to outline the spiral structure of the Milky way using all tracer data .

Methods : We collected the spiral tracer data of our Milky Way from the literature , namely , HII regions and giant molecular clouds ( GMCs ) .
With weighting factors based on the excitation parameters of HII regions or the masses of GMCs , we fitted the distribution of these tracers with models of two , three , four spiral-arms or polynomial spiral arms .
The distances of tracers , if not available from stellar or direct measurements , were estimated kinetically from the standard rotation curve of Brand & Blitz ( 1993 ) with R _ { 0 } =8.5 kpc , and \Theta _ { 0 } =220 km s ^ { -1 } or the newly fitted rotation curves with R _ { 0 } =8.0 kpc and \Theta _ { 0 } =220 km s ^ { -1 } or R _ { 0 } =8.4 kpc and \Theta _ { 0 } =254 km s ^ { -1 } .

Results : We found that the two-arm logarithmic model can not fit the data in many regions .
The three- and the four-arm logarithmic models are able to connect most tracers .
However , at least two observed tangential directions can not be matched by the three- or four-arm model .
We composed a polynomial spiral arm model , which can not only fit the tracer distribution but also match observed tangential directions .
Using new rotation curves with R _ { 0 } =8.0 kpc and \Theta _ { 0 } =220 km s ^ { -1 } and R _ { 0 } =8.4 kpc and \Theta _ { 0 } =254 km s ^ { -1 } for the estimation of kinematic distances , we found that the distribution of HII regions and GMCs can fit the models well , although the results do not change significantly compared to the parameters with the standard R _ { 0 } and \Theta _ { 0 } .

Conclusions :