Large-sized and optical-quality GdCa4O(BO3)3 crystal can be grown from melt by CZ pulling method. GdCOB is transparent in the range of 320-2600 nm. Second-harmonic-generation (SHG) experiments were carried out on the samples along (θ = 90°, φ = 46°) phase-matching (PM) direction in the XY-main plane and (66.8°, 47.4°), (66.8°, 132.6°) PM directions out of the main planes, respectively. The SHG conversion efficiency of an 8 mm long sample along (66.8°, 132.6°) PM direction was larger than 33% at 31 mJ input energy by a Q-switched Nd:YAG laser, which is the best result obtained so far to the best of our knowledge. The deff of these PM directions were estimated by comparing the conversion efficiency with that of KTP crystal, (66.8°, 132.6°) PM direction whose deff is 2.1 pm/v was reported for the first time as the optimum PM direction in GdCOB crystal. The angular acceptance and walk-off for these different directions were calculated, which shows GdCOB has a small walk-off and a large angular acceptance.