A transistor lasers have functions of both light emission of a laser and current control of a transistor and has many novel opto-electronic properties. Compared with short wavelength GaAs based transistor lasers， InP based long wavelength transistor lasers are more suitable for optical fiber communication systems. In this paper， the research progress of InP based long wavelength transistor lasers with emission wavelengths of 1.3/1.5 μm is introduced. The characteristics of long wavelength transistor lasers with different structures and the related device designs that can be used to improve the performance of the devices are discussed. Based on different waveguide structures， three types of edge emitting long wavelength transistor lasers have been reported up to now， which are shallow ridge， buried ridge and deep ridge transistor lasers， respectively. In the shallow ridge transistor lasers， multi-quantum wells are positioned in the p type doped base material. As a result， laser operation of an InP based shallow ridge transistor laser with 1.5 μm wavelength has been realized only at low temperatures. In the buried ridge transistor lasers， AlGaInAs multi-quantum wells are burried with current blocking InP layers. The fabrication process of the device is complex， which leads to a high cost. In the deep ridge transistor lasers， because multi-quantum wells are inserted between the emitter and the base layers， both the diffusion of p type dopant into the multi-quantum wells and the optical absorption of the p type base material can be reduced noticeably. Room temperature operation of InP based deep ridge transistor laser with 1.5 μm wavelength has been fabricated successfully. Numerical simulations show that by n type doping in the multi-quantum wells or introducing a current confinement aperture in the emitter ridge， the effects of the nonradiative recombination centers can be reduced greatly.