A comprehensive study on motion analysis and envelope of backhoe working mechanism of hydraulic excavator was conducted. Kinematic analysis formula of the working mechanism was deduced. Eleven different arc segments in the envelope of the backhoe working mechanism were described in detail. Envelope of a concrete working mechanism was composed of at most ten arc segments, and of at least six arc segments. Step function was selected as drive function of three hydraulic cylinders. A C++ program, which could generate drive function of the three hydraulic cylinders, was compiled. By changing dimension parameters of the working mechanism, six examples of envelope composed of from 6 to 10 arc segments were found by using the C++ program. Envelopes of these six working mechanisms were drawn.