8. (10 points) Calculate: $2013-2010+2007-2004+\cdots+9-6+3=$
Convert the expression to: $(2013-2010)+(2007-2004)+\cdots+(9-6)+3$, each group results in 3, and it is divided into $(2013-3) \div 3 \div 2+1=336$ groups, then multiply the difference of each group by the number of groups.

【Solution】Solution: 2013 - 2010 + 2007 - 2004 + $\cdots+9-6+3$,
$$
\begin{array}{l}
=(2013-2010)+(2007-2004)+\cdots+(9-6)+3, \\
=3 \times 336, \\
=1008 ;
\end{array}
$$

Therefore, the answer is: 1008.