The bearing capacity of circular shallow footings subjected to combined loading composed of vertical component V, horizontal component H and moment M on sand is explored through three dimensional finite element numerical analyses. The sand is assumed to be purely frictional and obey elasto-perfectly plastic relationship following the Mohr-Coulomb failure criterion. The capacity of circular footing under centrally vertical load is computed, and the calculated results agree well with those derived from slip-line field theory. Then the influence of soil friction angle on the failure locus in the V-H and V-M load plane and V-H-M load space is investigated. The results show that the shape of failure envelopes of shallow foundations on sand is different from that on undrained clay, whilst normalization of the failure envelope on the V-H and V-M load plane by the pure vertical bearing capacity allow it to be generalized for varying conditions. Based on finite element analyses, the equation of failure envelope in the V-H-M three dimensional load space is proposed, which can be used to evaluate the general stability of circular footings on sand under combined loading condition.