In this paper the spatial chirp and the angular dispersion for femtosecond optical parametric oscillation(OPO) are calculated theoretically and analysed. The analytical expression of the spatial chirp in the nonlinear crystal(BBO) is presented. And the analytical expressions of second-and third-order dispersions including angular dispersion of the nonlinear crystal for the noncollinearly phase-matched femtosecond BBO OPO in type-Ⅰ configuration with angle tuning. Moreover, variations of second- and third-order dispersions with the angular dispersion are calculated exactly.