The dynamics of the detachment of single polyethylene (PE) chain from a strongly adsorbing surface in vacuum is investigated by steered molecular dynamics method. When the chain is pulled from the monomer of N/3 (here N is the chain length), there are two force plateaus for the curve of the average force 〈f〉 probed by the ideal spring as a function of pulling distance Z，which agrees well with the experimental results. There are four different stages during the detachment of single polyethylene (PE) chains. As the chains are pulled in an inclined direction from one end, there exist always a linear relationship for average force probed by the ideal spring vs inclination angle θ for θ>20 degrees Furthermore, the slope of the line increases with the pulling velocity. However, for θ<20 degrees, the average force probed by the ideal spring tends to a fixed value of 780pN.