As one of mathematical representations of discrete distributed systems, Petri net has been widely used to model, analyze and simulate concurrent and distributed systems. The algebraic invariant is a powerful technique for the verification of Petri net. In this paper, we present a new and simple technique to construct the invariant of Petri net based on its properties. This technique can generate the invariant without computing DNF formula or Gröbner bases or using quantifier elimination, thereby circumventing difficulties in recent approaches. From the preliminary experiment results, the performance of this technique is significant.